Step 1: Get the game
You will need to get the original game in order to play online. You can try out the game for free by clicking this link
If you like the game, below you will find various stores where you can buy it.
Step 2: Download the matchmaker
The matchmaker is an application originally made to replace the now-extinct EA matchmaker to allow you to easily find other players to socialize and to play games with. It also adds a whole lot of other features such as: custom maps, rankings, 8 player support and much much more. The matchmaker is essential for playing online.