Go to Profile → Settings → Privacy to control who can interact with your content.
Private Account
When enabled, only approved followers can see your posts. New follow requests must be manually approved by you. Your profile will show a lock icon to indicate it's private.
Who Can Comment
Choose from: Everyone / Followers only / No one Controls who is allowed to leave comments on your posts.
Messaging
Direct messages are available after you Connect with someone. Follow is separate — Connect is the secondary action that opens messaging. You can further limit who can reach you from Privacy settings.