To play with friends (see Friends) you will all arrange to be logged in at the same time. One of the players will set up a table (see Start a Table) and the others can then join in.
Maybe you will use Whatsapp to keep in touch so that people are not hanging around waiting for latecomers. You can hold a 4-way conference call on Whatsapp so that you can do announcements, alerts etc. and also, if you like, discuss the hand afterwards.
If you are logged in when someone has reserved a seat for you at a table, you will see an invitation pop up.
If you wish to join, click on Yes at the bottom of the pop up.
It might happen that you log in to BBO after someone has reserved a seat for you. Invitations will appear in the People section and you may join the table from there.
To join, click on Join in the top right hand corner of the invitation.