The body of the pen unscrews at the "Moon Man" logo. You'll see an "F" or "EF" at the end of the metal part that touches the paper. It will be under where the body of the pen covers.
Okay, so good paper is important. The extra fine nibs will tear up notebook paper and lower GSM printer paper. Higher GSM the better.
Rhodia make wonderful notepads of varying sizes that work well.
No guarantee on card stock, fountain pen ink is very watery so it might not work well.