Help with balancing chemical equations and chemical equations?

A] have a look at http://richardbowles.tripod.com/chemistry/balance.htm
if you scroll down there are nicely animated examples

B] Single displacement
A chemical reaction in which an element reacts with a compound, and one of the elements in the compound is released as a free element. This can be represented symbolically as A + BC ?B + AC. Compare double-displacement reaction.

Double displacement

The reaction in which two compounds react by an exchange of ions to form two new compounds .a double displacement reaction usually occurs in solution and one of the products ,being insoluble precipitates out.

Combustion   equals burning

Synthesis making more complex chemicals from their elements or simpler molecules

Decomposition  substances breaking up