How to use a strobo?

Could anyone explain me how to set properly the ignition timing on my PX.

I´ve just fitted a Pinasco 213, and once I´ve fined the jetting I think I could avance a little more the timing, but I think I should know what I´m really doing dispite trusting on I.T and A marks.

Should I use a degree disk to set the TDC and a strobo, but how I do that?

Thanks in advance [:bounce:]