On your search results page you will have listings for interests, pages, people, topics, etc. You want to select the "Groups" tab at the top of the list.

Once you see the list of groups, choose a few to join that are Public groups (you have a better chance at being approved to join) and join ones that have a good number of members. See the image for examples:

Click the "Join" button on several, then wait for your approval notification (I usually get them within a few hours, sometimes immediately!)

One you're a member, it's time to check out the "competition" (hold for laughter)