Valve have introduced a crafting system which in addition to random item pickups during game now allows you to craft items that you want or need yourself.

 

Now click on the suitcase

This takes you into the backpack and where you can craft your hard earned items.

Now simply drag the items you want to craft from your backpack into the crafting area

And your newly crafting item will be awarded to you, make sure you accept it :>

Blueprints

Here is a list of the known valve blueprints for crafting.

Blueprint     Requirement    Produces
Smelt    Primary Weapons      3 Identical primary weapons     1 Scrap Metal
Smelt    Secondary Weapons      3 Identical secondary weapons     1 Scrap Metal
Smelt    Melee Weapons     3 Identical melee weapons     1 Scrap Metal
Smelt    Class Weapons     Any 3 weapons from the same class     1 Scrap Metal
Smelt    Miscellaneous Items     3 Identical Miscellaneous Weapons     1 Scrap Metal
Smelt    Tokens     3 Tokens     1 Reclaimed Metal
Combine    Scrap Metal     3 Scrap Metal     1 Reclaimed Metal
Combine    Reclaimed Metal     3 Reclaimed Metal     1 Refined Metal


Tokens


Blueprint     Requires     Produces
Fabricate Class Token     4 weapons from one class     1 Class Token
Fabricate Slot Token     4 weapons from one slot     1 Slot Token
Rebuild Class Token     One Class Token + another class weapon     1 Class Token
Rebuild Slot Token     One Slot Token + another slot weapon     1 Slot Token

Weapons


Blueprint    Requires     Produces
Fabricate Class Weapons     1 Class Token + 1 Slot Token + 1 Scrap Metal     1 Class Specific Weapon

Headgear


Blueprint    Requires     Produces
Fabricate Headgear     3 Refined Metal     1 Random Headgear
Fabricate Class Headgear     4 Refined Metal + 1 Class Token     1 Class Headgear
Rebuild Headgear     2 Hats     1 Random Headgear

For a more comprehensive guide click here