To add a friend to Funbelote, you must first go to the "My Friends" menu, accessible via the button on the far left of the banner at the bottom of the screen.
Once in the "My Friends" menu, you can see the friends you've already added. And those who are currently connected.
To add one of your friends to your friend list, you can click on the green "Search for a player" button. It will open a menu that will allow you to search for your friend using their nickname or first and last name if they have entered them in their profile. If the search is successful, the menu will display one or more results. Then select the profile you are interested in and press the green "Add" button. That's it!