Hi my name is Rem! How important is it to warm up before you sing?

Hi, Rem! 
I can't overstate how important it is! It doesn't need to be a long warmup, but you should always prepare your voice with something gentle like a lip trill, MM, NN, or NG. This helps to line up your vocal folds properly, reducing the risk of injury. A good warmup will gradually increase in difficulty - so you're doing the most demanding exercises (like belting) at the end. 

In addition to preventing injury, warming up will make your song work easier, I promise! Now, I casually sing throughout the day, and I may not be warmed up before humming to myself around the house. But I always warm up before spending time practicing a song, singing through my sight reading exercises, recording, etc. Once warming up is part of your routine, it'll be much easier to stick with!