PP will collect your bank account info and float a small deposit into your account to verify it. Then, when you do transfers, they'll debit your account. The verification process may take a number of days to complete. The instructions are on their site.
Being a verified user (at least years ago when I did it) supposedly increased one's respectability. Can't say about that anymore. You can add credit cards to your account to make payments that way too. Some sellers don't accept credit card payments or their PP account type won't allow them to.
As was mentioned, be sure to read PP's info on fraud protection and their security measures. IME, they will never ask an account holder for personal information in an e-mail or phone call which they initiate. They do request certain info to identify you in correspondence you initiate.
PP is a very convenient way to purchase items on [censored]. Just pay attention to the details....
I love PayPal! Buying Mustang parts with just a few clicks of the mouse can get expensive. Some sellers won't take PayPal through Credit Card because of the fees, that's why they want it through the bank instead.