Warm your milk (enough for one third full) on the stovetop or microwave. Roughly, 60 degrees.
Slowly insert the plunger and pump it up and down, whilst holding the top so the lid doesn’t lift off.
Keep plunging until the milk foams and expands to twice its volume.
Remove the plunger, and pour the milk into your coffee.
If you want to get fancy scoop some of the foam on top of your coffee, and create some latte art!