In Tomb Raider (the 2013 edition) for the PC, PS3, and Xbox 360, becoming more of a bad ass depends on you upgrading your gear.
Upgrading your gear requires two things, Salvage (the currency in the game) and Weapon Parts.
Salvage lets you purchase the abilities on a weapon, like Napalm Arrows or Explosive Arrows for the bow.
Weapon Parts allow you to upgrade your weapons to the next iteration of that weapon. For example, by collecting Weapon Parts you’ll upgrade the Makeshift Longbow to the Recurve Bow, etc. Each upgrade makes the weapon a little more powerful, and allows for more abilities to be purchased.
Salvage and Weapon Parts can be found anywhere that you get loot. Boxes, crates, dead bodies, etc. can all contain Salvage and Weapon Parts. Obviously Weapon Parts will be a lot more rare than Salvage.
As you’re collecting Weapon Parts, a notification will pop up telling you how many you need to collect for the next upgrade, and you can see your progress on the left side of the screen when you select that weapon under the Gear menu back at the base camp. Once you have collected all of the necessary Weapon Parts for an upgrade, simply sitting at the camp fire back at the base camp will automatically upgrade the weapon.
Upgrading the abilities on a weapon with Salvage is simple as well. Go to the camp fire at the base camp and select Gear, then select the weapon you want to upgrade. You’ll see the list of upgrades you currently have access to at the bottom, and the Salvage cost will show near the top right of the screen, along with a short description of what the ability does.
All unlocked abilities are carried through the weapon upgrade process as well, so upgrading your bow from the Recurve Bow to the Compound Bow for example won’t lose any of the abilities you previously purchased.