Influenza general background information
The human body is composed of cells - small compact structures which house our DNA. When we reproduce, our DNA is our body's blueprints and are passed onto our children. Viruses, on the other hand, can not reproduce alone. They use human cells to reproduce by "hijacking" human cells' machinery to make more viruses. These "baby" viruses are then either actively transported out of the human cell or cause the human cell to burst, releasing the new viruses into into the surrounding cellular environment.
The magnificance of the virus is that it is a survivor. It mutates (or changes) many times over in order to evade the human's system of detection. One type of virus is called the influenza virus or "flu" which commonly effects birds and mammals. Once the human body is infected by the influenza virus, the person is said to "have the flu". The flu is passed through the air by coughing or sneezing and common symptoms of having the flu include: chills, fever, sore throat, muscle pains, coughing, weakness and general discomfort.
Symtoms can vary and the duration can last for several weeks or even months depending on the body's immune system and response. Our bodies are equipped with multiple ways to detect viruses. In this, the virus's excellent survivor capabilities of mutation allow it to infect one person and, due to coughing and sneezing, infect several others. This is how the flu spreads.
Typical flu "season" is winter and precautionary measure including: frequent washing of hands, wearing masks if you are coughing and avoid public places if you know you are infected. Vaccinations against influenza may also be given. Typical vaccinations the TIV which is an injectin of a pre-killed virus or a live attenuated nasal spray called LAIV. But, because the influenza virus has the ability to mutate so rapidly, vaccinations would need to be given each year to be "up to date".