Shift/Brake Levers are also known as dual control levers. They have the ability of braking and changing gears in the same device. The most common style of shit/brake levers is to have the breaks accessable by squeezing your hand, with the gears being able to change by the movement of your thumb.
Road bikes shifters consist of a downward facing brake lever which when pulled activates the brakes and when pushed inwards towards the front wheel (like a pendulum) changes the gears of the front or rear derailleur (right lever changes rear derailleur and left lever changes front derailleur, vice versa in European style).
Mountain bike shift/brake levers use a horizontal brake lever and a “rapid fire” gear changing system. This system is attached to flat handlebars and consists of three levers. Two are within a short distance of the rider’s thumbs, which when pressed changes the gears to a higher or lower gearing ratio depending on what is required and the remaining lever activates the brakes which is located within short reach of the fingers.