When you are in a team you can add allies by running, they have to also run this command with your name to confirm that you are allies
/team allies add <name>

then give all your allies access to your claims with this command
/team config ftbu.blocks allies

To claim an area open your inventory and click the map icon

Then just click the chunk on the map

to chunkload the chunk SHIFT+LEFTCLICK the claimed chunk

To unclaim an area just RIGHTCLICK a claimed chunk

To give your friends access to your claimed chunks invite them with this command
/team invite <username>

After you invited your friend, he/she has to run
/team join <yourname>

If your friend is already in a team, he/she can leave it with
/team leave