"Red:
Left: How many you have in storage
Right: How many are in your truck/How many can fit in your truck

Magenta:
+ adds TO loadout
- removes FROM loadout

Yellow:
Tier indicator, count the pips; One big diamond = Tier 1, Two triangles = Tier 2; Three of whatever the shape was = Tier 3.

Blue(purple? May've picked a poor shade, just made this quickly)
Loadout contents. Currently you can see one filled in diamond for DOTS projector, the rest is empty.
Number of grey dots indicates how many can fit in the truck; IE, Video camera has 3 dots, Crucifix has 2, Firelight has 4.

Green:
Auto Buy: Auto buys anything missing from the loadout on next load to lobby, IE, When you die, or when you've used a consumable item.
Auto Add: Auto adds the loadout it's enabled on to the truck when entering the lobby.
Both can only be enabled on one loadout at a time.

Buy: Manual version of auto-buy; If it's lit up, you're missing something that the loadout needs to be filled out; clicking it will buy the missing items.
Sell: The inverse of buy; Use this to sell items... (why would you ever?)
Add: Adds the completed loadout to the truck; Once you've filled out your loadout, click it once; Don't try to go item by item- Fill out the entire loadout to your satisfaction and THEN click it.
Remove: Inverse of Add; Removes the loadout of items from the truck, provided they belong to you (You can't remove other players' items.)

Cyan:
Selected loadout is highlighted in yellow; Unselected loadouts are in grey. 'ALL' is just a fully fleshed out loadout. 1/2/3 are adjustable to your tastes.


How to use:
Click the +'s till you're happy with their quantity in the blue/purple box, once you've done this to every item, click add. You're done. Optionally, enable auto buy/auto add, and never worry about the shop section again.

You don't even need the 'Shop/Storage' section anymore, because you can fill a loadout to your satisfaction even without owning any of the item, just fill out the loadout, then click buy to buy anything missing."