The handle should have a screw in or out adjusting mechanism with numbers that show through a window.
They will be in foot pounds, inch pounds, or newton meters.
You match the number on the wrench with the recommended torque setting in the book, tighten it until it clicks and thats it.
You may have to convert some ratings when they are taking in a different standard ie inch pounds to newton meters but thats no big deal.
Also sometimes things like a cylinder head will call for 'step torquing'.
All that means is you have to tighten all the bolts down partially then add more torque to the wrench and tighten them all down again
and so on until you reach the full recommended torque rating.
Sounds complicated but it's really not.
A torque wrench is an investment everyone should have especially if you work on the motor yourself.