Inside this small wooden tower are two rocket launchers.  One is the Russian RPG (rocket-propelled grenade) and one is the American LAW (light anti-tank weapon).  Both of these weapons fire rockets, but they act very differently.  The LAW is a lightweight one-shot weapon, while the RPG is very heavy but you can replace the rocket on the front to fire it again.  Go up into the tower and fire both weapons to get a feel for how they work.  Note that you should drop the LAW after you fire it once since it will be spent.  After you are done continue up the path to the next Training Area sign.