Remove the adapter tool from it's holding feature on the lid and insert into a drill(cordless) or kitchen mixer. Place the plastic adaptor over the hex shaft in the center of the Lid. Mix in a clock-wise direction for 20-30 seconds and your paint is fully mixed.
Feel free to "Pulse" the trigger to pulse mix your paint, varnish or stain.
With the Lid/Stir still on the can, remove both caps, one to pour and the other to vent, and pour your paint into a roller tray or paint cup.
Replace both caps while you paint.
Repeat as needed until your project is complete.