An important defense against diseases in vertebrate animals is the ability to eliminate inactivate or destroy foreign substances and organisms explain how the immune system achieves the following?

Answer 1

Provides an immediate nonspecific immune response

I think this is talking about the physical barriers that stop a foreign substance from entering the body. Mucous, skin, hair... those are physical barriers that stop foreign substances from entering the body.

Activates T and B cells in response to an infection

There are two types of T cells, helper cells which help B cells, and Killer Cells which kill foreign substances. The T cells are activated when a phagocyte eats a foreign substance and takes it to the spleen to identify what the foreign substance is. The T cells make an antigen that binds to the foreign substance so the B cells can "kill" the foreign invader.

Responds to a later exposure to the same infectious agent

Sam process except it is more faster then previously. The immune system creates memory B cells that remember the foreign substance and it begins immune responses to fight off the infectious agent.

Distinguishes self from non self

It is all about the antigens. If the person has an antibody for a flu or something, it will fight that flu that has the antigen for the flu. If it has an antibody for something that is self that is called an autoimmune response which is not good at all.