What should I do with it?

I just switched on my laptop and this text came up. See image.
What should I do now?

That means that you don't have a Windows license. You will have to buy one if you want to remove the watermark (but you don't have to).

Follow the hint that is there and you will find out what to do.

Tip: Activate a legally purchased Windows license, either online or (I think you can also use the phone.

Well, I'm not very knowledgeable about things like that, but I think that's kind of a fresh start.
I'm sorry, I can't really help.