Primary immune response is what happens when the body is first exposed to a pathogen. So for the first few days there's little visable response from the body, but the foriegn antigen presence triggers the T-helper which then follows the full process down the chain.
Secondary immune response happens on subsequent infections, the body keeps memory B and T cells and has antibodies for the antigen. So the antibodies connect to the antigens preventing (or greatly delaying) the invading pathogen.
