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.