1.
to do sth in order to be certain that sth else happens :
Make sure (that) no one finds out about this.
They scored another goal and made sure of victory.
Our staff will do their best to make sure you enjoy your visit.
2.
to check that sth is true or has been done :
She looked around to make sure that she was alone.
I think the door's locked, but I'll just go and make sure.