Can someone please explain how you do aqueous reactions?

I am very confused on how you do aqueous reactions. I kind of understand double displacement but I dont really understand single displacement and combustion reactions. Please help! :)

the combsution reaction is when complete burning of a compound in presence of oxygen produces carbon dioxide and water , like 

CxHy + O2 --> CO2 + H2O


single displacement reaction looks like this

A + BC --> AC + B

but there is a rule that is always followedin single displacement reaction that is :  A metal replaces a metal, or a nonmetal replaces a example;

 Cu + 2 AgNO3   Cu(NO3)2 + 2 Ag

here  Cu displaces Ag in Ag(NO3)