You need a chair for this movement
Step 1
Keep your feet just wider than hip width apart (or a comfortable distance for you)
Step 2
Brace your tummy like someone is going to poke your stomach and keep your shoulders back with your chest up
Step 3
With your weight in your heels, squeeze your glutes (your bum) and sit down onto the chair
Step 4
Keeping your glutes squeezed and your tummy braced, stand up and return to your start position
Step 5
Repeat. As it becomes easier, spend less time on the chair until you’re just ‘brushing’ it rather than sitting