To play online, you need:
1) At least version 3.0 "WoW".
2) An opponent who also wants to play online.
3) A way to connect with the opponent.

The first point is quite clear. But just in case, here's a link to patches and the latest mods: http://equilibris.celestialheavens.com/rus/downloads.html
The second point is also not difficult. Your opponent must have the exact same version as you.
However, the third point is often where problems arise. The main one is that neither you nor your opponent has an external IP address. A way to solve this problem is to download Hamachi from http://files.hamachi.cc/HamachiSetup-0.9.9.9-ru.exe. Both players should install this program and join the same network. One of the players creates a game and selects a map, and the second player uses the opponent's IP address to connect directly.
If you have an external address, you don't need to install Hamachi; you can connect directly via IP, but you need to find out the IP address of your opponent beforehand. You can also play through Gamespy; the program eliminates the need to enter 12-digit addresses and connects you automatically.

P.S. You can easily see the IP address in the lower corner when the server has already selected a map.