How its supposed to work is that you download the client, enter a username, load the game and click connect. Other users who also did this and are playing on the same line as you will also be on the same line, and you'll be able to see the player ahead of you.
You'll probably be able to connect, but nobody will be there, as not many people play it, and the server will periodically glitch since nobody plays anymore. So the experience wont be as nice as you want it to be.
There is a better version that is in the planning stages, that will spawn multiple trains in the game, and will probably go back to the old server/client model. But lack of interest on both developer and users is what is really holding back the multiplayer OpenBVE.