The adverb literally means "actually," and we use it when we want others to know we're serious, not exaggerating or being metaphorical.
If your mom complains that your room is overflowing with clothes, she probably doesn't mean this literally. Your room might be messy and chaotic, but your clothes aren't actually piled so high that they're flowing into the hallway. Your mom is being figurative — she's exaggerating. Now, if your clothes really were piled up so high that they were flowing into the hallway, your mom would say, "Your room is literally overflowing with clothes!"