On Facebook, if I blocked somebody at first, can they blocked me too?

when you block somebody, they can no longer see or contact you, and you cannot see or contact them.

it is impossible to block what you cannot see.

if you block she or he from not connect you on facebook anymore. they wont able send you any more messages but if they were friends with your friends on facebook and she or he is friends on either ones lists instead you. still they can able to see your facebook timeline profile from the facebook search page and from your friends profiles friends lists. but wont tell the other person that you had blocked them. facebook doesnt tell that she and he had been blocked. only facebook knows that . i know that on messenger you can block unwanted vistors from your facebook but you need to go on search box and type their names then go to their facebook profiles and click on the right corner of the timeline and can click on where has telephone and webcam, icons on it then click one that has ( three dots ) then scroll  where say block. click that then the person wont able see and send messages to you when you are online. 

It is like God. You can't see him and he cannot see you.

Sometimes, you can block them back if they commented on your posts, even if they blocked you first (it's a FB glitch).

They cant Block you unless you Unblock them but Blocking is the same tho since you Blocked them they wont be able to get to your Profile at all 

Try it and see.