Chalk soaks up sweat so the bar stays put in your hands. Used well, it helps. Used badly, it makes a mess and does less than you think. Here is how to use it.
Chalk before you set up
Chalk your hands before you walk to the bar, not after you take your grip. If your hands are damp, dry them on a towel first. Chalk on wet skin turns into paste.
Cover the places that touch the bar
Work the chalk into your palms and the base of your fingers, where the bar sits. Rub your hands together so the layer is even. Your fingertips and the creases of your fingers matter most for a heavy pull, especially with a hook or a mixed grip.
Use a light coat
More chalk is not more grip. A thick layer slides and flakes. A thin, even layer works better and leaves less behind. Tap off any extra over the bucket.
Reapply when you need to
Chalk wears off with sweat and friction. On a long session, or after a warm-up that left your hands damp, chalk again between sets. For singles near your max, chalk before each attempt.
Do not chalk the bar
Chalk your hands, not the knurling. Chalk caked on a bar is a nuisance for the next lifter. When you finish, brush or wipe the bar if the gym provides a brush.
Try the grip you plan to use
Chalk does not fix a weak grip, but it makes the most of the one you have. If you pull with a double overhand grip, a mixed grip or a hook, practice that grip with chalk on your warm-up sets so heavy sets are not the first time.
When chalk is not allowed
Ask about liquid chalk. See liquid chalk vs block chalk for how they differ. Straps are a fallback for training sets, though they are not allowed in some meets, so check your federation's rules if you compete. Or find a gym where chalk is fine. Our list of gyms that say chalk is allowed shows the quote and source for each.
Clean up
Wipe the bar, tap your hands over the bucket and sweep up any dust. That small effort is why chalk stays allowed. For more on gym manners, see powerlifting gym etiquette: chalk.