An important thing to learn when learning to ride is how to mount your horse.
Whenever possible you should always use a mounting block to get on. This is not only easier for the rider but also and most importantly means that the process will put much less strain on the saddle and the horse's back. Mounting from the ground causes the horse to have to shuffle their balance to offset the rider's weight as they get on but can also cause the saddle to slip, twist and pull against the horse's withers. Another problem is that the continued pressure on the stirrup leathers can cause them to stretch. To avoid this you should swap them over regularly.
The textbooks always state that the horse should be mounted from the nearside however the reason for this is not clear, perhaps just tradition. Current research and many back specialists suggest that you should teach your horse to be mounted from both sides and alternate frequently. This is to prevent asymmetrical muscle development and repetitive strain caused by mounting continually from one side.
Before attempting to mount your horse it is important to check that your girth is sufficiently tight to prevent your saddle from slipping when your weight is in the stirrup.
If mounting from the nearside then face the side of the horse, level with the saddle and take your reins into your left hand. Using your right hand slip your left foot into the stirrup, turning the stirrup iron towards you in a clockwise direction. Make sure that the ball of your foot is on the stirrup. Then take the pommel of the saddle (the front) in your left hand and the cantle (the back) in your right hand. Stand up in the stirrup, releasing your right hand and swinging your right leg over the saddle. Make sure you sit down in the saddle very lightly. It is important not to plonk yourself down on the horse's back as their muscles are not yet warmed up and it will be uncomfortable.
Place your right foot into the other stirrup then lean forwards and check your girth by putting your fingers around it to see how much room there is. If it is loose then lift your leg forwards and pull the girth straps to adjust it.
Now that you're comfortable and so is your horse, you can ask the horse to move forwards.