Joining steam verion game with standalone

You could try to copy your Steam world into the world folder of the other version.

Does that mean you just want to load the world in the standalone version, or do you want to play multiplayer with both versions? If you just want to play the world: it's stored in the "Worlds" folder in the game directory (for the Steam version, it's in the "_New Version" subfolder). You can just copy it from your Steam folder to the standalone folder (or vice versa), as mentioned by Deirdre.

For example, if you have a world "My World", you can find a "My World" folder in your Steam game directory under "Rising World/_New Version/Worlds". Just copy the "My World" folder into the "Worlds" folder in your standalone directory

If you want to play multiplayer, however, you can either join a public multiplayer server, or download and run the dedicated server on your machine, or alternatively play a LAN game. You can't use the "Play with Friends" option because that only works in the Steam version (it uses Steams P2P), but after selecting a world, you can rightclick on that button to start a LAN game. It's basically like the "Play with Friends" option, the only difference is that it requires port forwarding in your router (unless you're playing in the same household). To join the game, you have to connect to the IP of the target machine (if it's a local game in the same household, the server browser should show the LAN game though).