1. Increased Strength & Power
Creatine helps your muscles produce more ATP (energy) during short, intense bouts of activity, so you can lift heavier or do more reps.
2. Better Performance in High-Intensity Exercise
Especially helpful for sprinting, weightlifting, interval training, anything with explosive effort.
3. Muscle Size / Hypertrophy
It promotes muscle growth partly through allowing more training stimulus (you can push harder) and also by drawing water into muscle cells (cell volumization). Over time, that plus your training leads to muscle gains.