Awesome game! As is mentioned, TNT is used for blowing up a target. On dod_omaha, the Allies have to take it behind the German cliff bunkers to the two bunkers in the left corner and take it into the door to blow up the target. In dod_dam, the Allies have to plant the TNT at the tank roadblock near the house overlooking the open area (just bump into the tank while carrying TNT).
Sticky bombs, on the other hand, are used to destroy tanks, such as on dod_caen.
It's still beta, ver. 1.1.