How much do you know already about the relationships between hardness, tensile strength, fatigue resistance, etc, under different conditions (such as annealed, normalised, fully hardened, etc) in relation to the various steel recipes? M2 is a steel designation, in the USA (and so, lots of places too), and H5 is a tolerance system for holes and spindles etc, but there is a long explanation for each of these terms.
Do you have access to any engineering reference books (such as Machinery's Handbook – there are others) where some of the terms will be explained? Or have you considered reference to Wikipedia, for example? And how well up are you in the world of metallurgy?
Sorry, but until we know quite a lot about your existing understanding, any explanation is likely – at one extreme – to be completely over the top, or so elementary as to be offensively patronising at the other.
Looking forward to a summary of how deep you have got, so far.
Regards, Tim