Practice is a game-mode available at the Ranch, that allows you to test the behaviour of units. A practice throws you into a fight where you have a team of three of the same unit; the opponent, a tin can, has a team consisting of three units of randomly chosen types. Units respawn in one tick. The opponent will keep getting units with random types while you will only get the type of unit you chose to practice with. There is no scenario, just a deathmatch without a time limit. The only way to end the match is to click End Practice Session or if either player's units all get killed before they can respawn.
Practice mode is always played on Training Corral, a small board, which contains a few terrain variances, and obstacles with which you can test your unit's movement limitations.