You need a Minecraft Java Edition account and an invitation from the game master.
Get an invitation code from the game master and register as a citizen. Use your exact Minecraft name.
Install the modpack with Prism Launcher (sign in there with your Microsoft account). You do this once; after that the pack keeps itself up to date.
Download the modpack. Do not unzip it.
In Prism: Add Instance → Import → Browse, pick the zip and press OK. Two mods do not allow automatic downloads: Prism shows them in a list. Click each link, press the download button on the page that opens, and Prism picks the files up from your Downloads folder.
Select the new instance, Edit → Settings → Custom commands, tick the box and paste this as the Pre-launch command:
"$INST_JAVA" -jar packwiz-installer-bootstrap.jar https://57-131-159-133.sslip.io/pack/pack.tomlIn the same window, under Java, give the game at least 4096 MiB of memory.
From now on every launch checks the Commonwealth for a new version of the pack (new voices, skins, mods) and fetches only what changed: a small window shows it for a moment. If it ever asks you to download a mod by hand, follow its link and save the file where it says.
You are whitelisted automatically. Registering puts your Minecraft name on the server's whitelist within a minute.
Connect to the server address shown on the front page.
Take the tour. It begins at the Wayfinder on the arrival square, where you arrive: the Wayfinder walks you through the whole Commonwealth, from the arrival square to the Square of the Revolution. Read and hear it first on the tour's page, or type
/cw tour startin the game.Open the Citizen's Booklet. It is in your pocket from the first day, and it leads to every service of the Commonwealth. Read the same booklet here, with every command of the game.
Read the rules before you play.