How to do a squat with a barbell?

Here's how to perform a barbell squat, incorporating the use of a box for depth control:

Setting Up for a Barbell Box Squat

Barbell Positioning: Stand under the barbell, ensuring it's resting comfortably across your upper back and shoulders. This position should feel secure and balanced.
Unracking: Carefully unrack the barbell, and take a few controlled steps back. You need enough space to squat and have a box positioned directly behind you for depth guidance.

Breathing and Bracing: Take a deep breath in to fill your abdomen, then brace your core muscles. This creates a stable base for the movement.
Initiate the Squat: Bend at your knees and hips, lowering your body in a controlled manner. Focus on sitting back as you descend.
Depth Control with the Box: Continue lowering your body until your glutes briefly touch the box. This is key for consistent depth. Note that you are not relaxing into the box but rather using it as a guide. The box can be set to a specific height to aid in training for squat depth.
Core Engagement: Throughout the entire squat movement, maintain a rigid core and stable back. Avoid relaxing as you sit or tap the box.
Standing Back Up: Drive through your heels to stand back up, maintaining your core and a straight back to the starting position.

Don't Relax: As the reference states, do not relax at the bottom of the squat. Keep your muscles engaged and maintain a stable, rigid posture.
Controlled Movement: The entire movement, from the descent to the ascent, should be done with control.
Proper Breathing: Inhale before the squat and exhale as you stand back up. Proper breathing assists in core activation.
Box Height: Choose a box height that allows you to reach the desired squat depth effectively, working on your squat depth.