To get into the Minecraft beta on Java edition on PC, you'll need to follow these steps: Install the Minecraft Java client by logging into your account and downloading it.

Minecraft Java Edition players can only cross-play with people on the same version, which is relegated to PC, Mac, and Linux.

This means that Bedrock players on PS4/PS5, Android, iOS, Xbox, and Nintendo Switch will have to switch to a PC to download and play the Java Edition, but they do get it for free.