Some basic coments
You need to add or set all your users (and passwd) on table "user" databases mysql with no rights (for each field set "N"). After that you must add your users on table "db" database mysql and there must set rigth that you need per each user and database:
see the samples here:
1). add or modify user in table user
insert into user values ("your_host"," your_user",password("your password"), "N",.......);
update user set your_fields="N"....... where user="your user"
add your users on table db.
insert into db value ("yout_host","your_user","your_database",....your rigths)
Sorry I'm not checked if the sintax is Ok,
Otherwise you use mysqlfront or webclient like "phpmyadmin" to do more easy that.
I hope that is enough