Trakt.tv allows you to follow other members of the community. If they follow you back, you are considered friends.
Navigate to the users profile page by clicking on a user's image or choosing Users from the dropdown menu of the search field in the upper left of any Trakt.tv page. Once you've navigated to their user profile page, click the Follow button. If the user has a public profile, you will be immediately following them. If they are private, they will need to approve your follow request.