Torque wrenches fall into three types: adjustable torque wrenches, portable torque wrenches, and preset torque keys.
Adjustable torque wrenches are high-precision workshop tools, some of which are found in the best mountain bike toolkits, that let you precisely preset the torque value you want to achieve before you start to tighten a bolt and give you a click as feedback once you reach it.
Portable torque wrenches are designed so that they're easier to carry than a workshop torque wrench, but still let you set a specific torque value, using non-preset calibrations on the tool.
Like an adjustable torque wrench, a preset torque key will also give you feedback when you've reached the correct tightening force for a bolt, but you can't adjust the torque value at which this occurs.