Registration in multisite

Hi to all, i’m new in this forum…
apologies to all if this topic is a clone of another…
I’m trying to develop a multiblog in wordpress
I have, for example:

1) http://mysite.com/blog1
2) http://mysite.com/blog2
…
n) http://mysite.com/blogn

My question is:
is possible to register user to single blog? (example: user1 registered to blog1 and his login credentials doesn’t work to blog2)

I hope I explained
thanks to all