Includes one standard .35mm diameter nozzle good for most printing.
Good for .25mm or less layer height, .35mm or .4mm extrusion widths.
Nozzles are a wear item. The plastic gradually wears the nozzle opening out, making it larger. It takes a good while for this to happen so it's not something to be too mundful of.
A spare nozzle is also handy in case something un-meltable gets dragged in with the filament and blocks the nozzle - it's easier to change it than to try to get al the plastic out and try to clear it. It may not happen to you... but it's sure annoying if it happens when you're trying to get a part printed in a limited time.