You have a dominant and non-dominant hand. If you are right-handed, your right hand is your dominant hand. If you are left-handed, your left hand is your dominant hand. If you are ambidextrous, choose one hand to use as your dominant hand, and stick with it.
There are three types of signs when it comes to what hand you will use:
One-handed signs: Uses only your dominant hand
Two-handed symmetrical signs: Uses both your dominant and non-dominant hand where they both move the same way
Two-handed non-symmetrical signs: Uses both your dominant and non-dominant hand where the dominant hand moves while the non-dominant hand remains stationary
Your non-dominant hand will never move unless your dominant hand is moving the same way. This is very important for when you graduate from basic sign language into more complex signing. You don't want to get confused!