So…
I want to reset my laptop because it is way too slow for me. So if I reset everything and then enter my Windows key, which I entered on my laptop before, will I still have Windows 10 or do I have to buy it again?
You don't need to buy Windows 10 again.
Simply reinstall, enter the key, done.
So if I completely reset my laptop, then I only have to enter the key and nothing more?
This is usually not required for you to enter it again. After reinstalling Windows it either works by itself or you choose "I don't have a key". It will then still be activated. A Windows key is linked to the built-in hardware. So don't you exchange e.g. The mainboard will be recognized by your system and the Windows key assigned to it will be released again. But yes, you can use the (on the same device!) Again.
If you reinstall Windows, but don't change the hardware, you don't even need to enter the key. Microsoft stores the key for your hardware. You can skip the entry. Windows will still be activated.
