Antibodies are produced when the body is exposed to antigens.
During an initial encounter with a foreign antigen, the body's immune system namely the adaptive arm of the immune system, produces memory cells, a group of special lymphocytes that retain and store memory of the antigen.
On a second encounter with the same kind of antigen, the immune system "remembers" the antigen and mounts a rapid, specific and vigorous immune response against the antigen. This response includes the production of massive amounts of antibodies very specific to the antigen.
The antibodies effectively neutralize the antigen and facilitate its destruction.