Great question. I recently did this, myself.
All you do is go to the sign-up page, type in a person's email and then type in the password that you want to use...and then hit submit.
That is all it takes to create an account. Your friend will then get an email notifying them of the account creation.
Now...you still need to tell your friend what the password is.
So, just repeat that process as often as you like. If you want 20 accounts created, then sign up 20 times. I would recommend using the same password, so you can keep track of things. And then your friends can change the password once they log in.