PHP order form

I've created this order form for our site: [login to view URL] Right now it's just a dummy form that doesn't do anything. What I want it to do is this: 1. Check to make sure all of the required fields are filled in, and correctly 2. Take the coupon code, check it against some sort of database (which also needs to be built). Apply it to whatever the final cost is. I also want an attribute to count the times each code is used, and to update this when ordering. 3. If they choose to pay with Paypal, go to a Paypal checkout form (Paypal account will be supplied) 2. Email me the info they fill out, as well as their IP address 3. Email them the attached order confirmation. 4. Direct them to [login to view URL]