One of the great things about MAc OS is that so much of what you need is already baked in, unlike “other” operating systems which will go unnamed. You know who you are horrible OS that still uses 8 bit DOS calls.
In order to access your Mac (or allow us for support or training purposes!) you simply need to enable the VNC Server in Mac OS X. Instead of reinvent the wheel, I will let the good folks at http://www.dssw.co.uk have their due and point you to their brief but excellent guide which can be found here.
Here is the YouTube video, click the link to get the full writeup with screen shots.