To give a little bit of context from another implementation, NodeBB implements a follower system like ActivityPub.

Out of the box we don't have the concept of "friend", but if we think of the usage as that of early Facebook, then a "friend" relationship implies a reciprocated follow... similar to a LinkedIn "connection".

In AP-land, that'd be a follow-accept and then a follow-accept from the other direction. Whether this is completely automated or manual is dependent on the implementation, I suppose.