Screen sharing on a Mac simply involves selecting the Mac you want to share in Finder, clicking Screen Share, then logging in. If you're looking for an even faster method, Macworld shows you how.
The process here just requires you to make an alias:
[U]se the method you've used in the past to share the Macs screen... When the [other computer's] window appears take a gander at the shared screen's title bar where it says something like Jim's Mac mini and drag the icon that appears just to the left of that name to your iMac's desktop. A VNC alias file will be copied to that self-same desktop.
That's it. Now you have quick, easy access to screen sharing right on your desktop.
How to create a Screen Sharing Shortcut [Macworld]