which salts are soluble in acids and which salts react with acids? 
Well, for example:
HCl will be able to displace HNO3 from a nitrate salt, but HNO3 will not be able to displace the stronger HCl from a chloride salt.
another example,
HNO3 is more reactive than sulphuric acid, so HNO3 will displace a sulphate salt
Also...
CuCO3 (contains carbonic acid which is a very weak acid) + H2SO4 --> CuSO4 + H2O + CO2
It depends on the strong acidity of the acids reacted
About which salts are soluble inside, calm down that is not necessary in IGCSE i guess

~
just learn the basic insoluble and soluble salts

good luck