Accessing a computer on the same network as your iPad, iPhone or iPod touch is usually just a matter of entering the local network IP address or computer name when prompted in the apps discussed below.
However, accessing your computer from outside the home or office is more complicated. You'll need to configure your router so that the relevant ports are passed through to the computer you want to connect to. You'll find guides online. It's also wise to configure a dynamic DNS service so that you can connect via a hostname rather than an IP address, which is prone to changing. Examples of dynamic DNS services include NoIP and DuckDNS, which are free of charge, but how they're configured is again outside the scope of this article. There's many guides available online — just search using your router model number and "dynamic DNS".
Setting-up your Mac and iPad for screen sharing
Mac OS X uses the established Virtual Network Computing (VNC) protocol to share a desktop remotely, so any iOS app that supports VNC will work. There are quite a few of these, in fact, but one of the best that also happens to be free is VNC Viewer. It can be found in the App Store but before using it you'll need to configure the Mac you want to connect to: put a tick alongside Screen Sharing in the Sharing component of System Preferences, then click the Computer Settings button and ensure there's NOT a tick alongside either of the two headings you see.
Note the address listed beneath the heading that reads Screen Sharing: On. You'll need it to connect in a moment. It's also a good idea to note your Mac's IP address in case using this address doesn't work — click the Apple menu, hold down Alt (Option on some keyboards), and click System Information. In the window that appears click the Network heading in the list at the left, and look alongside either Wi-Fi or Ethernet at the right depending on which your Mac is using.
On the Mac you'll need to note either your computer's name or it's IP address, as highlighted here
Connecting to your Mac or PC from an iPad or iPhone
On the iOS device open the VNC Viewer app and click the plus icon at the top right. In the dialog box that appears, type the address you discovered in the paragraph above, and in the name field type something memorable and identifiable such as Mac Desktop.
Click Done, and then the Connect button. You'll be warned you're using an unencrypted connection. This is unfortunate but there's no way to avoid it, so tap the Connect link at the top right of the window. You'll then be prompted for the username and password of the Mac account you want to log into. You should type the "short" version of your username — usually your first name, or the first whole word of the longer version of the username.
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