Your very first step to learning ride is learning to get on the horse. The first few times you get on a horse, have someone hold the horse's head so that it stands quietly. You can, and should be able to get on from the ground, but a mounting block makes it easier for you, is better for your saddle and is easier on your horse's back. If your horse is tall and your legs are short you can drop the stirrup a few holes so that you can reach it with your toe, or you can use a stirrup extender. Don't forget to re-adjust the stirrup leather to the proper length once mounted.