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.
Lead your horse out of the stable. It is unsafe to get on a horse in a confined area with low roofs or doorways. If you are riding English, run the stirrups down the leathers so they are hanging free.
Here are the steps your coach or instructor will take you through. Don’t worry, getting on isn’t all about strength. The first few times you’ll feel like getting on is a struggle. But, you’ll soon learn to use your balance to help you spring into the saddle.