How to launch minecraft 1.7.9?

I got a pc downloading card at bestbuy for MINECRAFT.

I run the launcher app and the login screen pops up(so far so good) after loggin in.

I got the screen where you have at the bottom the big PLAY button.

I press the Play button and I got the log in screen back again(I'm into a loop here)

How do I fix it.

(I'm not computer savvy so, please don't be very technical (as possible)

Alright, so first off youve got to go to the minecraft.net website where you will have to click on the buy button thats to the right. Then you will have to create a new account like it asks you to. Next up, when you get to the buy or redeem page, you should have a code on the back of your download card thing. Put that in and get it registered. Then you should download the launcher and use the login information to play. Hope that helped.