Gain accuracy thanks to the added friction between the cue and the ball.
Why put chalk on billiards cues?
What we call chalk is actually an essential accessory. And for a single simple reason: putting chalk on the tip (the end of the cue that hits the ball) gives it a better grip.
So what? So chalk makes shooting easier, lets you put spin on the cue ball, and prevents miscues (when the tip of the cue slips on the ball causing you to miss the shot).
Most people scrape the chalk on the cue's tip, which prevents the chalk from spreading out. Instead, you should rub the tip with the chalk while checking that it spreads evenly.
Good to know: effect of chalk on balls
After each shot, a small amount of resin is left on the ball. Therefore, you may eventually consider polishing the balls (using an appropriate product or a specialised machine found in billiards clubs).
On a more practical note, remember to place the chalk open side up on the table to avoid getting your table dirty. There are also magnetic chalk holders that you can use to hold chalk in your hand throughout the game.