Quetoo has multiple gameplay modes all centered around blasting your friends to bits. You'll have to frag your "enemies" and stay alive to be successful. Learn to use the map and the items available on it to your advantage. Stock up on weapons, ammo and armor like they're going out of style, and always know where the nearest health packs are.
Classic deathmatch. There's many players but no teams in this gamemode, so just shoot at everything that moves and expect others to do the same. The rough idea in this mode is to frag as many opponents as possible without getting yourself killed too often. The player who reaches the fraglimit first (fraglimit setting) or the player who has most frags when the timelimit is hit (timelimit setting) is the winner.
Teams-based deathmatch play is a long-standing favorite of all veteran Quake players. Up to four teams occupy the map: Red, Blue, Green, and Orange. Use the banner at the bottom of your screen and the scoreboard to know which team you're on, and go after the other teams. Communication is key in this gameplay mode, so you may want to setup some say_team macros to help out. Friendly fire may or may not be enabled, so ask before your teammates become collateral damage.
Again multiple teams fight against each other in this mode. Each team has a base that holds its flag. The idea is to steal the enemy flag and take it back to your base. You can only score a capture if your own flag is still at your base, so make sure it is defended at all times. If a flag carrier is fragged they will drop the flag. Run over it to teleport it back to your base (if it's yours) or to pick it up (if it belongs to the other team). Captures, not frags, are the goal of this gameplay mode, so taking one for the team is sometimes wise.
In Rocket Arena mode, players spawn with full armor and most weapons and ammo (the BFG is not supplied), but that's all you get. No pickup items are available to replenish you. In addition, self-damage is disabled. This means that you can rocket jump and grenade jump and without taking damage. Use this to your advantage to out-maneuver your opponents and reign hell upon them.
Instagib is the low-pinging-bastard (LPB) game of choice. Players spawn with only the railgun and infinite slugs. Like Rocket Arena, no pickup items are available, so don't bother looking for them. Each rail shot is an instant kill, making this a very fast-paced gamemode. Point and click your way to victory in this fast-paced, reflex-rewarding gameplay mode.