Immune system help

Hello, I have some questions about the immune system.  I dont really understand how it works...I've recently became really interested becuase I have anxiety of throw up, and someone in my family is sick and I just want to know how the immune system works.  Is it something that gets weaker over time? Or can it be weak some days, and then be strong other days? I just really dont understand how it all works.  
Also, what makes an immune system weaker? or stronger?

[Hopeless29]

It is all upto the RBC & WBC, White Blood Corpuscles has an effective role though in terms of immunity.
those scientific things apart,If u feel weaker mentally or emotionally then u may presumpt u r weak physically, and when u think u r weak physically even when u r not sick u may fall into conclusions that u r weak when u r actually not, by the time when u r taught its jus an illusion, u might fall sick(a Slight fever or cold) presumably or definitely which helps u wrongly believe that u r short of immunity and u will remain sick forever, and forces u too catch up enumerous forms of phobias leaded by a prominent one which u r more convinced of, as in ur case emetophobia.

[twitch01]

the immune system can work in different ways but the way it mostly works is to help fight off infection. it can start out stong but it can get week when your a baby it is week and that is why they say to keep the baby away from germs it is easy for it to get sick. but yes if your immune system gets week it can get stronger of a period of time and with some medication