If you're on Desktop, look to the top left and you should see a column titled Browse, look down this Column for Activity. Under this you should see options for My Activity Streams, click on this and you will get some default choices like Unread Content, Content I Started, Content I Follow, etc. If these don't suffice you can build your own custom queries using the Create New Stream button at the foot of the list.
If you're on Mobile, in the top right you will see 3 horizontal bars, tap them. As above, go to Activity. Under this you should see options for My Activity Streams, click on this and you will get some default choices like Unread Content, Content I Started, Content I Follow, etc. If these don't suffice you can build your own custom queries using the Create New Stream button at the foot of the list.