After a year or two, depending on the speed of improvement, a white belt becomes a blue belt. Getting a blue belt means that the defense is getting a lot better, and as a blue belt, you will start to learn combinations and be much more confident in your BJJ skills.
A blue belt improves on techniques such as leg locks, collar chokes, and half guard sweeps. As a blue belt, you must have a guard that is hard to pass, control the opponent from the mount, know various side control variations, etc.
It is very important to learn that the blue belt takes 3-5 years to master, so usually, there is a big difference between a “beginner” blue belt and an advanced one. IBJJF (International Brazilian Jiu-Jitsu Federation) requires from a person to be a blue belt for at least 2 years and be at least 16 years of age.