ok, I ask again.. how to encrypt to be able to match database info?

I've asked this several times but it doesn't seem like anyone understands my problem, the passwords are encrypted in the database, but I don't know how to match an unencrypted password from the login form with the database? is it possible to encrypt the password I sent from the form in php or does that have to be done in mysql? in any case, how do I do it? If you don't have anything bright to say, don't, in some of the replys I've had earlier it sounds like you think I'm an idiot... And even if I am, I don't want to be refered as one ;)