A comma is a “soft stop”. It’s not a final as a period. It’s used to connect new ideas to old ones, and to tell the reader when to pause a moment in their thinking (or in their speaking, if they’re reading out loud). In long sentences, it’s also used to separate clauses, so the reader understands which modifiers apply to which words, etc.
Michelle’s parents are very, very proud of her.
I only slept for five hours last night, but I’m not tired today.
Despite the snow, the buses are running on time.
For dinner, there’s meatloaf, red potatoes, and green salad.