I've been given a couple of weapon unlocks, but how do they work? How do i get that weapon?
If you're asking how to unlock them, when you log into the game again with that account, it will have a pop up window which you can scroll through the classes with and choose which one(s) you want to unlock.
Now assuming that you already did that^^, then you must be asking about how to get them ingame. To do that, on the spawn/class selection screen there is a little button on the upper right corner of each class with an up & down arrow on it. Click that arrow button to cycle between the standard and unlocked weapons for the classes you have it available on.