For individual or team practice, you regularly need your own server. If you haven't rented or created a server yet, you can use the in-game tools.
At first, you create a lobby. All you have to do for that is invite a friend, and a lobby will be created automatically. After that, you need to set the next settings: game mode "casual", lobby type "private" and choose a map. In addition to that, you need to setup the game itself, too.
After that, you need to gather all players together in a lobby and start the game. This way you'll get a casual 5×5 match. In order to make it competitive, you need to activate a certain config. For example, you can use an ESL config, which is used at all tournaments by this organizer. Use the command exec config name to active a config.
That's it! It'll take only five minutes to setup your own tournament-format server. However, there's a problem. You can't add modifications to such a server and, for example, play the retake mode. Next time we'll talk about creating your own server outside the game.