Marvin uses a symbol/quick word language to allow anyone to quickly enter details about a task or project.

List of task input shortcuts

So for example to create a task (Call insurance) that is due in 5 days and has a label "quick" and is a "Household" task you would write:
"Call insurance @quick due 5d #Household"

The order in which you add the attributes does not matter!

The nice thing about a symbol shortcut is that as soon as you type the symbol you get a dropdown menu to quickly select what you mean: 

You can edit the title of an item anytime to add additional attributes.