if you add someone to friends do they have to accept or are they just added?

you can 'follow' someone, which means you'll be able to find/see their posts more easily. if they reciprocate, it'll then call you 'friends', the person you follow can also elect to block, remove you from following them, or do just let you follow.

You become their follower. Then, they have the choice to remove you. If they remove you... you can never become their follower again.

You have to send a dk pic before they will accept you

Check your friends list every so often. If you get a "newcomer", check his profile before you acccept him or her. If their interests differ from yours, block and delete them. Don't allow trolls to harrass you!

It is only an option to add you back. It is common courtesy to do so, however.
If someone adds me I check out their profile first before adding them back. For the most part, I never hear from them.

They can choose to accept, ignore or block.