Oscilloscope Newbie

Hi gang,
An old analog philips has come my way, and I'm looking forward to getting better acquainted with the boombox technical side of things. I have a question or two about input cables. I can't work out why the probe has a little tunable cap to calibrate it to the scope input, but if you're using say bnc to phone cables on the inputs for azimuth purposes (it's dual channel) you don't have to worry about that kind of thing.

Also what kind of coax cable should I be using? 50ohm rg58?

Sure would appreciate the answer to these conundrums.
Thanks

Please do not take me at my word as I know nothing on the subject. I am sure there is someone here that is capable of providing the information you need.

In my neck of the woods 75ohm RG59 is more available.

pretty sure the answer is 50ohm cable for audio hookups (done more research)