It's the informal, second person singular form of the verb "aller" (to go).
Here are some examples of how "va" might be used:
* Va à l'école. (Go to school.)
* Va te coucher. (Go to bed.)
* Va voir ce que j'ai trouvé. (Go see what I found.)
It's important to note that "va" is an imperative verb, meaning it's a command or instruction.