line up the 3 dots, 2 eyes with the scope dot in the middle... been shooting the Muellers for years, best bang for the buck I've found... are extremely clear for daylight shooting also... probably wouldn't need it but since I've gotten used to it, no use to not use it...
the Muellers use a CR2032 battery, a common watch/electronic battery... I use it in my red dot sights, bike speedometers, blood sugar meters also... buy them on fleabay, a 10 pack for just a couple bucks... very easy to find, if you go in a store that carries batteries, if it has any of the flat types, the 2032 will be there...