The party is on!
Why this never was an option from the start, we never understood. The days of waiting in a queue to join your friends is over. In the game, select Multiplayer. You should now have the "BF4 Squad Join (Beta)" option. If you click it, you will start in the lobby. (see image below)
Join or start a squad
When you are in the lobby you can see from the squads created by your friends. There are 5 spots available per squad. If there is a spot, join the squad. (see image above)
To create your own squad, select "New Squad". A new squad will be automatically created. When your friends are in the lobby they have the option to join your squad. When you filled up your team, hit the square button to jump into any available server with spots for your team. (see image below)
Select the Game Mode
If you click the triangle button, you will have some options. At least, that is how it appears. Probably during the Beta, DICE decided to keep the options limited to "Game Mode" only. (see image below)
You can always join your friends using the Battlelog option. Press "Select" button on your PS3 controller, select a friend in the squad and click the X button.