To block someone is a very difficult decision. but if you want to do this , follow my instructions.
open a profile of a user or page you want to block. and click on top option to get options men like this
select option "Block" like this
if you are clear enough to take a decision then select option "yes i am sure " like this
now if you want to see whole list of blocked persons.
go to your Instagram profile and click on top right option to go to settings menu like this
now select option "blocked users" like rhis
you will get a list of blocked users like this
if you want to unblock it. then click on blocked user. its profile will open. and click on top right option like this
now click on option "Unblock" like this
it will ask you whether you are sure or not...
click on " yes i am sure"
ans user will be unblocked...