Marijuana
Collecting (Cannabis)
To collect Cannabis head over the the Weed Field (Green 'Weed' On map) Once you have arrived walk up to a plant and Press E to begin harvesting. Repeat this untill you are finished. You can store them in a vehicle by looking at a vehicle, Pressing Y and dragging the item to the right hand side
Processing (Marijuana)
To Process the Cannabis into Marijuana, head over to the Weed Processor, When in the correct area you will have the ability to press E to Process 1 Cannabis into 1 Marijuana. Repeat untill complete.