welcome to the forum Fresh P

There is plenty of information on superheat on this forum if you use the search on the forum toolbar.

Briefly though

superheat = amount of energy in a vapour above its boiling point measured in degrees of temp.

suction sh is ambiguous so I'll describe it as

evap sh - measured directly after the evap
suction sh - measured at the suction line near to the comp.
discharge sh - measured near the discharge of the comp.

To measure you must know the pressure, the boiling point of that refrigerant at that pressure and the actual temp. of the refrigerant at that point.

then sh = actual temp - refrigerant temp.

if the answer is less than 0 then you have sub cooling.