Sit on the ground and place your hands on the sides, in front of the hips.
Push on your hands to lift your butt off the ground, so that only your hands and heels touch the ground.
Form tips
Push your shoulders down ( Shoulder depression ).
Keep both legs straights.
If you think your arms are too short (which is very unlikely), try the Chair l-sit ; if you manage to perform that exercise, it is a muscle activation issue, not an arm length issue.