Privacy settings

Who can see your account, who can reach you, and what your presence gives away.

All of this is in Settings, then Privacy.

Account visibility

Private profile
Only followers see your posts, followers and following. Everyone else sees your name, photo, bio and counts.
Show followers list
Whether others can see who follows you.
Show following list
Whether others can see who you follow.
Suggest account to others
Whether you appear in suggestions and search results.
Show who viewed your profile
Reciprocal: off means you cannot see your own visitors either.

Presence

Active Status
Shows when you are online. Off means you also cannot see anyone else's.
Invisible Mode
Appear offline to everyone while still seeing others' status.

Messaging

Allow message requests
Whether people you do not follow can reach you at all.
Read receipts
Reciprocal. Turning them off requires Sapphire.
End-to-end encryption
On by default. See Encryption.

Security notices

Login Alerts email you when your account is accessed from a new device or location. Leave them on.