The human genome does not contain the DNA to create every single Antibody. Somatic recombination is used to semi-randomly shuffle the genes, which code for antibodies when B cells become immunocompetent (Marieb).
B cells stick their antibodies out of their cell membranes as a receptor. When an antigen bonds with the antibody, it triggers the primary immune response. The B cell multiplies (only B cells with 'good' antibodies multiply, hence the name clonal selection). This is a form of evolution. Most of the 'children' which are identical to the original, become plasma cells. These produce thousands of antibodies over the course of 4-5 days, then die. This period can last longer during the secondary immune response. B cells produce some antibodies, but not nearly as many. A few of the B cell's children do not become plasma cells. They remain identical and wait to bond with another antigen and will do the same thing as their parent when they do. These cells are called memory cells, and are capable of mounting a faster, more effective, secondary immune response, if the antigen ever becomes present again.