FOSS gamedev and creative worlds

When I want to register for minetest, where do I go? I am having trouble to actually play. I tried this account but it didn't work.

Each server, being owned and run generally by different people across the Minetest community, has a different registration method, though usually you just have to make up an in-game name and password, and use those each time you sign into that server.

Some servers go a bit further - for example, on mine you have to make a forum account first (which you already did). On redcrab's server, there's a semi-automated sign-up via email.

Also, please be more specific, "it didn't work" is not enough information.

Minetest does not have global accounts like Minecraft.
You can choose whatever name you want when you connect to a server. Also the passwords are only stored on the server you connect to, so you can use completly different names and passwords for different players.