Looking at the vault on DIM, I have approximately nine hundred thousand, billion, billion, billion, billion, billion, billion mods in my possession. But so far, the game hasn't explained how I can use these things or where. So far, it seems like Rares can't be modified at all, and Legendaries can only modify the elemental damage type. How does this all come together? Is there a website where I can learn more about this stuff? Can anybody here tell me what I can do with them?

Honestly, don't bother placing blue mods on anything. Once you hit 280, you can turn in 3 of any of the same blue mod to get a random legendary mod from the Gunsmith, which adds +5 to the Power Level of whatever you put it on, so it's a decent little bump up.

Mostly, they don't seem that useful, and seem to be a pretty poor substitution for the old perks that were on gear in D1.

Mods are basically the perks on armors from D1. Feel free to equip them as you play along at lower levels because you'll get so many blue ones anyway. Some boost your armor/recovery/movement. Some abilities like melee or grenade. Some weapon handling etc.

Weapon mods are mostly modifiers of energy types. Keep all your purples for stuff you really wanna keep. They usually come with a power/light level boost for the item it gets equipped to.

Blue mods are just materials to make purple mods. Every 3 blue mods turns into one purple mod. If the gunsmith has a purple mod for "sale" in the bottom row of his vendor screen, "buy" it, which will convert 3 of your blues into purps. Purple mods increase the item power of your assigned item by 5, which helps with leveling.

Purple gun mods determine if a weapon is elemental or not. That's it.

Purple armor mods can add minor perks, such as faster grenade recharge or better kinetic weapon stability. I do not know if mods of the same type stack or not.

There are also class-specific mods for your hunter, warlock, and titan. If you don't have one of these classes, just delete the mods for that guy. Otherwise you can vault them.

I have a bajillion mods as well, but the gunsmith only shows 12 total purple mods that I can purchase. I want to make a purple solar mod, but its not showing solar, just arc and void. Nothing changes when I reopen his inventory. Anyone figured out the exact way to do this yet? Or am I missing something

• Use Legendary mods to break 280. That +5 is useful. That's +4 power levels if all your gear has one.
• Take all Rare Mods and aggressively convert them to Legendary when you hit 280.
• Identify which legendary mods you won't use (looking at you Paragon Armor mode) and break them down for 1 Mod Part.
• 2 Mod Parts + 1k Glimmer buys you a new Legendary mod. This is the best way to get Kinetic mods as you cannot get Rare Kinetic mods.
• Rare mods are a great glimmer dump once you can convert them into Legendary mods.