How to Craft Items
Before you can craft an item, you should see what materials you'll need to craft it. You can check what an item is crafted with using the item command.
The assault_rifle requires that you are at least level 9 and have 1x metal, 1x metal_spring and 2x rifle_body. Once you have these items in your inventory you can craft an assault_rifle using the craft command.
How to Recycle Items
Some items are able to be recycled for materials, you can check if an item can be recycled with the item command. If you want to recycle the item, just use the recycle command!
Checking What Items a Resource Can Craft
You can see all items a materials can be used to craft with the item command, ex. t-item metal would show all items metal can craft:
You can also check what an item can be used to craft on the items page.