Java Edition users of Minecraft will need Java installed. After doing that, you’ll need to download the version of Minecraft Forge that matches your server version.

You can install mods in "Minecraft" by playing the "Java Edition" and using the third-party app Minecraft Forge.

As of today, the cross-platform version Minecraft Bedrock has launched "add-ons" through its in-game marketplace which, yes, are essentially also mods, free and paid.

If you want to play Minecraft with just your friends, the easiest way to do so is to run your own server.