I place an LED in Pin 13 and GND,
Well the first lesson to learn is to never wire leds to output pins without series wired current limiting resistors to protect both the led and the output pin from damage. As you learn basic electronics principals you will learn and understand what you should and should not do. Trying to learn basic electronics my memorizing a lot of rules of do and do not topics is a very poor and error prone method of learning electronics fundementals.
But of course I felt compelled anyway to give you such a do not do 'rule', because I don't want to help you destroy your arduino output pin before you understand why you must use resistors with leds.