This is the PayPal link I use which is on eBay, here's the link http://www.ebay.com/paypal/buyer/protection.html?ssPageName=MOPS123:PayPal
Once you follow the instructions in signup and have an account, there is an link for "pay". That's where you can pay someone using their PayPal account name.
I have used PayPal alot on eBay, but with my credit card. I am pretty sure there is an option to use your checking account too. I know I over-simplified this, but I hope it helps.
BTW, I only use the PayPal link from eBay because there are some bogus look-alike sites out there.