Brake levers & shift levers at good prices from starbike.com
Shift levers actuate the front derailleur
and the rear derailleur
which change the gears.
The gear change is transmitted via a tensioned cable to the derailleurs, which then move inwards or outwards.
Shift levers are available as trigger shifters or twist shifters
The latter ones are popular among many mountainbike
The brake levers
operate the bicycle brakes
and are always handlebar-mounted. There are mechanical brake cable systems and hydraulic disc hoses.
You can find a wide selection of different brake and shift levers, e.g. from