You have your opponent in the guard.
To try and escape your guard, your opponent stands up to cause pressure on your crossed feet.
Uncross your feet and pull your knees down. Now press your knees together infront of your opponents stomach. Also cup round the back of your opponents ankles with both hands as shown.
Now thrust your knees up to cause your opponent to lose their stability and pull their ankles towards you. Be sure to push your knees directly upwards.
As your opponent falls back you should come up on your right hand, twisting your body slightly sideways, and reach across their body with your left hand. Try to grip their arm or body with your left hand to help pull yourself up.
Continue the movement so you end in the mounted position.