when you join by default everyone is assigned "not particularly interested" value and your feed is simply based on notes that are most often reposted, quoted, liked and so on.

as you read this content you can check out the profiles of people posting it and adjust their value.

eventually those whom you rated higher than "not particularly interested" will push other content down the timeline.

you never "follow" or "unfollow" everybody.  you simply TUNE your timeline from a purely algorithmic one ( based on global engagements ) to one that reflects your personal preferences.