The antibodies neutralize the invader or mark them for destruction by other immune cells. When the antigen is gone, suppressor T cells send chemical messengers to T cells and B cells to slow down or stop their activity, thus ending the immune response.
Once a B cell has made an antibody, it presents the antibody to other white blood cells so they can read the blueprint and know which invader to attack. If the same antigen tries to invade your body in the future, your memory B and T cells will recall this antigen and quickly destroy it.