Crafting in Reign of Terror has a lot of the same aspect as the base game. It can be used to help fill out your gear when you are looking for that last piece you need. Crafting in RoT can be done right away from level 1 by visiting the Anvil in the Rogue Encampment right next to Charsi.
Gear that can be crafted using the anvil:
There is an anvil in each town, so don't worry about going back to Act I to craft gear.
Blueprints can be found from any monster. They will drop just like any other piece of gear, or loot. Right click these items to "Learn" the blueprint.
Once learned you will be able to craft that item indefinitely.
Blueprints are account-wide, meaning what you find on one character can be crafted on every character.
There is a massive amount of blueprints availible. From low level ones that you will never use, to high level end-game ones that can be a game changer for your character.
I suggest running the Shattered Realm to start finding end-game blueprints (lots of them I might add)
The Anvil in the Rogue Encampment
Example of what the anvil opens up too
Just a few categories able to be crafted