It's an informal way of encouraging someone to start something or move forward. It's often used to express enthusiasm and excitement, similar to phrases like "Let's do it!" or "Let's get this party started!"
For example:
* "Vamo que, o jogo vai começar!" - "Let's go, the game is about to start!"
* "Vamo que, a gente já está atrasado!" - "Come on, we're already late!"