Engage your core, hinge at the hips as you lower the bar, keeping your spine neutral . then drive your hips forward and use your hamstrings to power back to standing position.

Weight Recommendations:
Beginner: Try just the bar first or dumbbells

Intermediate: 10-35lb plates on each side of the barbell
Advanced: 35-66+lb plates on each side of the barbell

*Modification: use dumbbells instead