If you are just learning to use the genoa, and if your boat has a knotmeter (speedometer) then the easiest thing to start with is to go out on the water when the winds are not very strong. You will need a crewperson to help. Set the mainsail traveller car so that it is in the dead center of the boat and adjust your mainsheet so that the boat is sailing with very little heel, as close to the wind as you can get.
At this point it doesn't matter where your genoa car is (as long as the genoa is up and the genoa sheet is going through the block (pulley) on the genoa car). Start moving your car back and forth and look at your knotmeter to see what effect it has on your boat speed, also note what it does to your angle of heel, and how close your boat can sail into the wind. Don't adjust the mainsail at all, and have your crew maintain as steady a course as possible. Use your genoa to control your boat.
Then tack - without touching the mainsail - and experiment again on the other leg. Giu has explained the theory of it for you. Print his post and take it with you so that you can understand how it affects your boat. You may find a slight difference in adjustment is required between port and starboard depending on how true your keel is, how much weight there is on either side of your boat, and how evenly tuned your rigging is. Then again - you might not notice anything for a few years
Keep practising in various types of wind and water conditions. You will be surprised at how quickly you start to develop a feel for your boat. Expect to find a difference between the two Genoas, as the difference in size changes the location of the center of effort on the boat. Enjoy