Tennis rackets recommended stringing tension generally ranges from 40 to 65 lbs (18-29 kg).
Lower tensions (40-50 lbs) provide more power and/or comfort due to the “trampoline” effect.
Higher tensions (60+ lbs) offer greater control and precision.
If you are unsure where to begin; I suggest to starting in the middle of your rackets recommended tension range. Once you have found your preferred string, I would then suggest playing around with your tension. Easy analogy: Your tennis racket is the car, the strings are the engine and the tension are the tyres.
I mainly measure tension in pounds due to the finer scale but it is purely a preference.
jwstringing.co.uk 