To view a list of all the groups that you've joined, you have two options.
First, you can see a complete list of all the groups you've join in the bottom half of you left hand navigation menu.
Or, you can view the Groups page of your profile. Here's how:
1.) Click the dropdown arrow at the top of the left hand navigation menu
2.) Click on View Profile in the dropdown menu.
3.) Click on Groups in the page header. This will display all the groups you've joined.