Set up and use screen sharing
While your screen is being shared, the user of the other Mac sees what’s on your screen and can open, move, and close files and windows, open apps, and even restart your Mac.
Set up screen sharing
Choose Apple menu > System Preferences, then click Sharing.
Select the Screen Sharing checkbox.
If Remote Management is selected, you must deselect it before you can select Screen Sharing.
To specify who can share your screen, select one of the following:
All users: Any of your computer’s users can share your screen, except sharing-only users and guest users. If your Mac is connected to a network account server, anyone with an account on that server can share your screen using their network user name and password. For more information, see Join your Mac to a network account server.
Only these users: Screen sharing is restricted to specific users.
If you selected “Only these users,” click the Add button
at the bottom of the users list, then do one of the following:Select a user from Users & Groups, which includes all the users of your Mac except sharing-only users and guest users.
Select a user from Network Users or Network Groups, which includes users and groups with network server accounts. Network users and members of network groups can use their network name and password to connect to your Mac for screen sharing.
To set additional options for screen sharing, click Computer Settings, then select one or both of the following:
Anyone may request permission to control screen: Before other computer users begin screen sharing your Mac, they can ask for permission instead of entering a user name and password.
VNC viewers may control screen with password: Other users can share your screen using a VNC viewer app—on iPad or a Windows PC, for example—by entering the password you specify here. If you select this option, you should create a very secure password.
Share the screen of another Mac
If you’ve been given permission, you can view and control the screen of another Mac on your network.
Before you start, make sure the Mac whose screen you want to control has screen sharing turned on.
Open a Finder window. If no shared computers appear in the Shared section of the sidebar, put the pointer on the word Shared, then click Show.
Click All to see all available computers, then double-click the one whose screen you want to share.
Click Share Screen.
If both computers are logged in using the same Apple ID, the screen sharing session starts. If they’re not, you’re prompted to enter the user name and password of a user who is allowed screen sharing access on that computer, or you can request permission to share the screen if the computer allows it.
If someone else is already connected to the Mac as a remote user, a dialog asks if you want to share the display with the other remote user (Share Display) or log in concurrently using a different user name and screen (Log In).
If you choose Log In, you share the Mac with the other remote user, but you won’t share the same screen.
If you know the IP address or the DNS name of the Mac you want to share, you can also connect to it by choosing Go > Connect to Server in the Finder and then entering vnc://[IPAddress] or vnc://[Name.Domain] in the Server Address field.
To find the address of a shared Mac, open Sharing preferences on that Mac, then select Screen Sharing.
Set screen sharing preferences
When you’re sharing the screen of another Mac, you can set screen sharing preferences to adjust the size and quality of the shared screen.
Start a screen sharing session with a Mac on your network.
Choose Screen Sharing > Preferences, then set the following options:
Under Display, select “Scale to fit available space” or “Show full size,” depending on how large your screen is and how much of it you want to use for the shared screen. This option changes the default behavior for when you share the screens of computers you’ve never connected to before. To change the current scale, choose View > Turn Scaling Off or View > Turn Scaling On.
Under Display, select a “Scroll the screen” option to determine how the screen sharing window behaves when you move the pointer. To decide which option you want, try each one by selecting it and then moving the pointer around in the window.
Under Quality, select “Adapt quality to network conditions” to view the shared screen more quickly, or “Show the screen at full quality” for a more detailed view of the shared screen. This option changes the default behavior for when you share the screens of computers you’ve never connected to before. To change the current scale, choose View > Adaptive Quality or View > Full Quality.
For the best results, and if your Mac is connected to a fast network, view the screen at full size and show the screen at full quality.
Under Blocked Users, choose an option from the “Allow screen sharing requests from” pop-up menu to enable sharing your screen with either everyone who tries to connect to your computer using an Apple ID or just your contacts.
To block users with specific Apple IDs from sharing your screen, click the Add button
, enter the user’s Apple ID, then click Block. To unblock users, select them in the list and click the Remove button 
.
Set view options while sharing another computer’s screen
When you’re sharing the screen of another Mac, your viewing options depend on your network connection and the size of the screen you’re sharing.
Start a screen sharing session with a Mac on your network.
From the View menu, set the following options:
Show Tab Bar: Use this option to display or hide the tab bar.
Turn Scaling On/Off: With scaling on, the entire screen of the shared Mac is displayed on your screen. With scaling off, the shared screen is displayed full size, and might require you to scroll to see everything on the shared screen.
Switch to Observe Mode/Switch to Control Mode: In Observe mode, you can watch what’s happening on the shared screen, but you can’t control the pointer, move windows, open and close documents, or do other tasks. If you’re observing OS X v10.9 or later, you can click and hold to highlight the screen at your pointer. In Control Mode, you control the shared screen.
Adaptive Quality: Use this option if your Mac is connected to a slower network. Adaptive quality adjusts depending on network speed.
Full Quality: Use this option if your Mac is connected to a fast network and you want full resolution.
Show/Hide Toolbar: Show or hide the toolbar that displays buttons for adjusting the scale, sharing the Clipboard, and other options.
Customize Toolbar: Drag buttons into or out of the toolbar.
Enter Full Screen: The screen sharing window expands to fill your screen. To see the toolbar and menus, move the pointer to the top of the screen.
Displays: If the Mac whose screen you’re sharing has more than one display, you can choose which display you want to view.
Share the contents of the Clipboard with another Mac
When you’re sharing one computer’s screen with another computer, you can transfer information between the Clipboards of the two computers. For example, you can:
Copy text and images from documents on one Mac and paste them into documents on the other.
Select and drag text and images from one Mac to the other.
Copy a link from your web browser and paste it into a web browser on the other Mac.
Copy text from a document on one Mac and drop it on the desktop of the other Mac to create a clipping.
Start a screen sharing session with a Mac on your network.
Choose Edit > Use Shared Clipboard.
You can also use Universal Clipboard to copy text, images, photos, and video on one Apple device and then paste the content on another Apple device.
Send files while sharing another computer’s screen
When you’re sharing one computer’s screen with another computer, you can transfer files between the two computers.
Start a screen sharing session with a Mac on your network.
Select a file or folder, then drag and release the files over the screen sharing window.