Measuring tension on bolts?

Have two questions regarding the "torque" that is recommended by the EGO user manual when tightening a mower blade back into place, or, when replacing it. Here is the info: Place a metal rod (e.g., a manual screwdriver) into the fixing hole to act as a stabilizer, then use a 9/16 inch (14mm) torque wrench (not included) to tighten the bolt clockwise. The recommended torque for the blade bolt is 36-43 ft-lb (49-59Nm) (Fig. 21). Questions: 1) How do you measure the amount of torque you put on a bolt and what tool (or tools) can be used to measure it? 2) And, what does 36-43 ft-lb (49-59Nm) mean?