I'm assuming by make database he's talking about storing the info or some such work.
As far as making sure that people are only included once you just need to do a simple for+if statement to check that the names in all of the other slots are not the same as the name being added. you have to use .equals() for this instead of == or it won't work though.
As far as making sure that people are only included once you just need to do a simple for+if statement to check that the names in all of the other slots are not the same as the name being added. you have to use .equals() for this instead of == or it won't work though.