New to 3D Printing

Hello all. So I bought a Prusa i3 kit off of eBay and have finished the build. So now what? I have researched online and it sounds like I need a firmware to run this printer. I believe that I am somewhat intelligent when it comes to programs but this time I'm lost. I downloaded Marlin, Arduina, and Printrun but the lack of instructions is frustrating.

Do I need firmware to run this printer or can I just use the SD card slot?

Is there a "dummies guide" to using this printer?

What steps do I need to complete to get this up and running?

Thanks for your time.

I also bought an Prusa i3 clone (a Tronxy X3).
It uses a Melzi board and runs Repetier firmware.

Have you gotten up and running?
Whose printer do you have?
What controller board do you have and what firmware did it come loaded with?