Parenting a newborn is like playing a weird, exhausting guessing game. For the most part, all they do is eat, poop, pee, cry, and sleep. It's impossible to communicate with them, so you soothe their cries, fill their tummies, and lull them to sleep, hoping your efforts will assuage their discomfort or anger. It takes some time to decipher their coos and cries, but when you do you'll start to notice the ways your baby is trying to say "thank you," long before they're actually able to say the words.
Trust me when I say that a day will come when your exhausting, needy, adorable, but overwhelming baby will start showing you their gratitude, and when that day comes you will feel all the things. You'll start to notice that your baby wants to be held all damn day long, which can be so exhausting but also their way of saying, "Thanks, mom! A solid snuggle is just what I needed." They'll smile the moment they look at you, reach for you when you come into view, and cry when you walk out of the room. They will demand you — and no one else — at bedtime. The first time they say "mama" will break you in the best possible way.
Being a mom is often a thankless job. As your kids grow, and learn how to use their words to tell you how they feel, you probably won't get all the credit or thanks you deserve. So, while you can, you should definitely watch for all the ways your baby is trying to say "thank you," before they are able to say anything at all.