I am new to the game and just bought Guild Wars Factions and my question is... where in Cantha ( the mainland ) could u get a capture signet to capture the elite skill flesh golem and how to i capture it?

To get a capture signet you need to go to a skill trainer. I believe there is one in the main port(forget the name of the city) that has it. Now to get the skill you first need to find the boss, there is a topic about that in the skills forum http://forums.photics.com/showthread.php?t=2591
Then after you kill the boss use the signet and select the skill from the list that will pop up after you use it.

The main port is called Kaineng Center - the skill trainer there have the Signet of Capture for sale. To use it to capture a skill, simple kill a boss that have the skill you need, and then use the signet near the boss. A window will appear with all the skills the boss has - you can either choose one and that skill will permanently replace your signet of capture or cancel the window and keep your signet of capture.
note that you can have multiple signets of capture at once in your skill list and your action bar

Thanks alot guys this really works! and i caped it!! thx!!