1-First press ENTER to get the message line.

2-Press + and enter one of the following codes.

3-After entering the code press ENTER to activate the code.

To deactivate a code just enter it again

Code:  -   Effect:

+ATM - Gives you 1000 metal and energy.
+CDSTART - Starts CD Music.
+CONTOUR# - Displays a 3D contour, # = 1-15.
+CONTROL# - Lets you to control a different skirmish AI.
+DITHER - Dithering instead of line of sight.
+DOUBLESHOT - All weapons do twice the damage.
+HALFSHOT - All weapons do half the damage.
+ILOSE - Causes you to lose.
+IWIN - Causes you to win.
+NOENERGY - Drops your energy to 0.
+NOMETAL - Drops your metal to 0.
+NOSHAKE - Stops explosion screen shakes.
+NOWISEE - Full map and disables line of sight.
+RADAR - 100% radar coverage.
+SING - This command makes units "sing" when given orders.
+SWITCHALT - Allows you to switch between squads with alt+# keys.
+VIEW# - Lets you see how much metal and energy a player has. 

Below is the first Campaign cheat code:

Click on Total Annihilation's Single Player icon. When the Single Player 
Game page appears type DRDEATH (it is not case sensitive). This will 
cause a Cavedog Entertainment bone to appear between the Load Game 
and Previous Menu icons on the right side of the screen. Clicking on the 
bone will take players to a special Play Any Game screen where they 
can play any Total Annihilation mission, even if they have not earned their
 way to that level yet.