IcarusGuideIcarus is joined from inside the game: pick a character, choose Join, then Dedicated Servers, and either search for your server by its name or use Direct…
Icarus is joined from inside the game: pick a character, choose Join, then Dedicated Servers, and either search for your server by its name or use Direct Connect with the address on your server card. If you set a password, every player types it. A brand new server opens in the server's lobby, where the first prospect is started. Joining never touches your saved prospects.
Your server's name or address. The address is the colored strip at the bottom of your server card on My Servers, the hostname with its port after the colon. Click it to copy it. The name is your Server Name, on the Basic tab of the Overview card.
The server password, if you set one. It is optional for Icarus: the Server Password on the Basic tab, left blank, lets anyone who finds the server in. To copy it, click the small arrow at the right end of the address strip and use Copy password (on a phone the pills sit under the address and this one is called Password).
A server that says Online. A sleeping server does not answer, and trying to join does not wake it. Press Wake up on the dashboard first (What is Wake and Play?), or let friends wake it from your public page (Let friends wake your server).
The same shortcut row has a How to join pill that opens this guide (on a desktop it is behind the arrow at the right end of the address strip; on a phone the pills sit under the address).

Start Icarus from Steam and pick a character. Characters stay on each player's PC and work on any server.
Choose Join, then Dedicated Servers.
Either search the list for your server's name, or use Direct Connect and paste the address from your card exactly as copied.
Type the server password if the game asks for it.
If Direct Connect does not take the address, search the Dedicated Servers list for the server's name instead. The name in that list is the Server Name from your dashboard; after you change it, it shows there from the next start.

On a desktop browser, while your server is Online, click the small arrow at the right end of the address strip. The Join pill with the Steam logo launches Icarus through Steam with your server's address. Treat it as a shortcut: it may only open the game, and then you join from Dedicated Servers as above. The pill does not appear on a phone or while the server is asleep.
That is normal. An Icarus server holds saved runs called prospects, and when none is running (a brand new server, or one with Auto-Resume Prospect off) everyone who joins lands in the server's lobby, where a prospect is created or loaded. Icarus: Prospects, Open World, and the server lobby explains the lobby and the three prospect settings, including who may start a prospect.
Icarus is a PC game on Steam, so your server is for Steam players on PC. There is no console or mobile version of Icarus to connect from.
The server is missing from Dedicated Servers after an Icarus update. RocketWerkz patches Icarus every Thursday, and the game's server list hides servers on another version by default. Your server moves to the new version when it restarts once nobody is playing; restart it yourself to skip the wait (Start, stop and restart your server), then search again or use Direct Connect.
"Wrong password" or the game keeps asking. Copy it again from the Copy password pill. A changed password applies on the next start.
A modded server. Every player needs the same mod .pak files on their own PC: Icarus: Install Mods.
Everything else (timeouts, stuck connecting, it works for you but not a friend): walk through I can't connect to my server.
Ask in Discord or email support@haptic.gg. Include your server name, which way the player tried to join (the list, Direct Connect or the Join pill), and a screenshot of the message they get.