To calculate the resistor you need to know some parameters regarding the LED.
Normally a red LED has a forward voltage of approx 2volt and a current of 20mA and the output from the Raspberry Pi is 3,3volt.
This means that 1,3volt (Raspberry voltage - LED voltage) and 20mA is the values for the resistors. then lets take 1,3v/0,02A = resistor (65ohm).
And what GPIO pin to use, well that's up to which pin you fancy in the programming.
Take a look at this video series, that will explain a lot: https://www.youtube.com/watch?v=OR5h0UnMcUE
Table for LED,voltage vs. color