Your mileage may vary depending on your learning style, but I got started with Godot from their official guide on creating your first 2D game. Their manual is also the gold standard for what you can do with the engine. It's a lot to digest, so if you look at the docs and find them a little bewildering that's normal. I mostly use the manual as a reference once I already have an idea what it is that I want to do.

If you like video tutorials, I like these guys. Their courses regularly go on sale, and they can help you hit the ground running. You can probably find a bunch of videos on Youtube too, but again, your mileage may vary. I would note that when learning from video tutorials, you're usually taught how to do things, but they often miss out on the why behind them.

If you're a reader, you can find tons of books on game design here. They have a few books on Godot as well, although one thing to watch for is what version of engine they use. Most of the books I found cited 3.0 when we're now on 4.2.

One of the perks of being an open source engine is that there's tons of demos and the like online. Here's a collection of demos which you can download the source code and check out yourself. You can even play them in the browser to see if there's one you like and want to build upon yourself.