When it comes to weight training, compound movements like the bench press, squat, and deadlift are the most important exercises, helping you to develop a good base of muscle and strength. Having a good form when performing those exercises is a crucial thing, not just because it will allow you to progress faster, but it will keep you away from injuries.
When you start to perform this kind of compound movements, it can be pretty easy, but with time, the weight on the bar will start to feel heavier and heavier, and progress will be a lot harder. During hard lifts, your core plays multiples roles, and it’s really important to learn how to use it properly. The core has to be braced at every single repetition, this way you will have better stability and your spine will remain neutral. Learning to brace your core correctly during heavy movements will help you to improve a lot, and most importantly, will keep you away from lower back injuries.
Think about it like this, if you see that someone is going to punch you in the stomach, what is going to be your first reaction? You will probably brace your core, letting as much air as you can enter your stomach.
This is exactly what you have to do during compound movements, this way your core will act like a wall that keeps your body stable. Brian Alsruhe explains this technique really well in this video.
One of the most frequent mistakes is to just flex the abdominal muscles, like you would do when taking a picture, for example. Doing this is better than nothing, but it’s not the most effective way to use your core.