The Armory was introduced in the US version of Armed Assault or 1.07 beta patch for most other people. The Armory is like a big single player mission that allows you to test out and familiarize yourself with the different units, vehicles and weapons available in the game. When you first have a look at the Armory you will notice that many items are locked. The goal here is to run through some of the training exercises, by completing these you will unlock additional units and vehicles. Another way to unlock items on the list is by completing the single player campaign and or some of the single player missions.
You can also play with the Armory with third party addons. For optimal compatibility, mod-makers can configure their content for the Armory.
One way to save time during these missions is to speed up the game using the acceleration button (-/+). You can speed up the game walk up to your objective much quicker.
Using the RHIB
Once you have unlocked one of the RHIBs, you can aim the boat away from the islands and press and hold both the "vehicle forward fast" key (default is 'e') and the escape key to send the vehicle into the endless sea while automatically rejecting any primary challenges. The RHIB is fast enough to complete all secondary challenges (worth ten points each) and a new item will unlock per 20 secondary challenge completions (200 points). On a time acceleration of 4x, you have about 15 minutes of fuel and should accumulate 400-700 points after which you'll have to abort and re-enter or accept a primary challenge to get a full tank of gas.
Unlocking All Gear
There's a cheat to unlock all gear instantly if you don't enjoy unlocking it by playing normally. See ArmA:_Cheats.