Craft

A true craftsman has brains enough to use his aesthetic senses tastefully.

Used for creating items with or without recipes, making nice graffiti and putting mods on weapons. Some of the items you can create require workbenches to assemble. Cooking for example requires a stove of some kind.

Without a recipe, you can try to see if you can make something out of an item using: improvise with <item>
And then when you figure out what to make it with: improvise <project> with <item>

The best way to grind craft is to use the license plate press in prison. Grab an npc or player in sight of the cameras to get a quick sentence, then walk in, grind your craft, and pay a small fine to leave. Of course, you could go all the way and kill someone, but you'll be making "friends" for a longer time.