Ok when you start UT, select File, Practice Session, pick which maps you want to play, what settings you want to use (translocator, speed, air movement, etc...) and then select how many bots and at what difficulty setting. You can even configure all of the bots individually to have their own unique traits such as preferring to camp, being aggressive, fearful, etc... I assume you've been playing the ladder so far? That's a good way to get familiar with the game, but the only way you can customize the number of bots in the game without using console commands is to play a practice session as far as I know. Hope that helps ya out.