The catalyst lowers the energy necessary to get a reaction started. These are surface or contact catalysts. They are typically metals or metal oxides. The catalytic converter in your car has a heterogeneous catalyst in it. These are catalysts that are in the same state as the reagents.
Biological catalysts are enzymes.
Electron transfer reactions are chemical reactions where the reagents change oxidation number. A net ionic equation shows that particles that react and the particles that form in a chemical reaction. It does not show the spectator ions. Spectator ions are ions that do not change from reactants to products. A precipitation reaction involves a cation and an anion coming together to form an insoluble salt.