1. Go to https://www.minecraft.net/en-us/download
2. Wait for the page to load
3. Under "Select your preferred Linux distribution", choose Debian. It should download 'Minecraft.deb', and it'll probably put the file in the 'Downloads' folder.
4. Quit your web browser to save memory (the laptop sadly doesn't have very much and Minecraft probably needs lots of it).
5. Run these commands (noting that Linux is case sensitive for filenames, so preserve the case):
cd Downloads
sudo dpkg -i Minecraft.deb
sudo apt-get install -f
Note: Make sure to preserve the case for filenames as Linux is case sensitive.
6. Now, in the Applications menu, look in 'Games' for the 'Minecraft Launcher'. Run it, and it will download the Minecraft launcher. You might need to wait a while, between 10 and 20 minutes. Make sure the laptop charger is plugged in.
7. After that, you should see the Microsoft Account login screen. If you don't see it or if it is acting weird, you might benefit from rebooting the laptop and starting 'Minecraft Launcher' again.
8. Eventually, when you log in with your Microsoft account, you'll get into the Minecraft launcher. Click "Play" at the top. It will start downloading the Minecraft game itself. This will take between 10 and 20 minutes.
9. If it says "Oh no! something went wrong, and we couldn't connect to the Minecraft services." at the bottom, if you can see that the download is still progressing, just ignore that message. As long as the download is working, it's okay. Wait and see what happens.
10. If something goes wrong during the download, just click "Play" at the top again and it will hopefully restart the download.
11. Eventually, Minecraft should launch. Then you should be ready to play. You will need a mouse to play the game properly. Note that it will take a while to start a new single player world, it has to generate the terrain or something. It might take between 10 and 20 minutes.
12. Once the game is running, press Escape, go to Options, Video Settings, and reduce the simulation distance to between 7 and 10. You may need to change other settings to improve performance, experiment a bit.