Now that you are on board there are a couple of things that need checking before you can ride. The first is to check the tightness of the girth. You may only have tested it 30 seconds ago before you got on but now your weight is on the horse's back it will probably need taking up.
Take both reins into one hand and move your leg forward past the knee roll of the saddle. You can see Pam's foot is still in the stirrup. You will now be able to lift the saddle flap and reach down to the girth straps and adjust them as necessary.
If this is your first time in the saddle this can seem a strange manoeuvre which makes you think you'll lose your balance. Your instructor will check and tighten your girth for you until your balance improves.
If you got your stirrup twisted around the right way before you mounted it should lie along your leg like this,
If you have it twisted the other way the leather's edge will try to dig into your leg.
Your instructor will help you set the stirrups to a suitable length. As it all feels quite odd at this stage you will probably not be able to judge for yourself if they are of equal and correct length.
Next - using a mounting block.