Dan give a great explanation of what is called N,N- and N+ development and the reasons for it but if you are brand new to analogue film taking and processing then don't worry. If you expose as your hand-held or in-camera meter suggests and develop as the film manufacturer recommends for that film and its developer you will get very printable negs. Film is very forgiving. You are not on a knife edge where not being able to control everything or a small error results in negs that may as well be thrown into a bin

Take things one step at a time and enjoy it. Things will be fine