What are the basic components of the immune system

The immune system is made up of the Innate (or non-specific) immune responce and the acquired (or specific) immune responce. 

Imagine you live in your castle and it is your job to protect it. First you'll have your first line defence, a moat and a wall. Then you'll have a net and a trip wire to raise the alarms. If the attacker manages to make it through all of this then you will need a specialist defender. Someone who has seen this attacker before and knows how to defeat him. 

Now imagine that your body is the castle and the attacker is a pathogen. The moat, wall, nets and trip wire are parts of the innate immune responce. The moat is your normal flora, these are the microorganisms which lie on your skin, they help keep harmful pathogens out of your body. The wall is your skin. Once the pathogen has got through the first line defence your phagocytes ( the net) come into play. These are cells which eat foreign cells if they recognise that they are bad. They also help to call the acquire immune system. The trip wire is the inflammatory responce. This is a system that brings many cells to the site of the problem, they raise the alarm. 

The specialist defenders are the acquire immune responce. This is made up of the B and T lymphocytes. These cells have memory and know how to kill specific pathogens. The B lymphocytes use antibodies to destroy pathogens and the T cells can kill cells by using chemical mediators. 

The immune system is complex and you can explore each component in huge detail. But it is very important to get a good general overview of the immune system