Helper T cells are actually quite important and interesting. They are activated by Interleukin-1, produced by macrophages. Once activated, Helper T cells produce Interleukin-2, then interferon and other chemicals. These chemicals activate B cells so that they produce antibodies. The complexity and level of interaction between neutrophils, macrophages, T cells and B cells is really quite amazing.
Because white blood cells are so important to the immune system, they are used as a measure of immune system health. When you hear that someone has a "strong immune system" or a "suppressed immune system", one way it was determined was by counting different types of white blood cells in a blood sample. A normal white blood cell count is in the range of 4,000 to 11,000 cells per microliter of blood. 1.8 to 2.0 helper T-cells per suppressor T-cell is normal. A normal absolute neutrophil count (ANC) is in the range of 1,500 to 8,000 cells per microliter. An article like Introduction to Hematology can help you learn more about white blood cells in general and the different types of white blood cells found in your body.
One important question to ask about white blood cells (and several other parts of the immune system) is, "How does a white blood cell know what to attack and what to leave alone? Why doesn't a white blood cell attack every cell in the body?" There is a system built into all of the cells in your body called the Major Histocompatibility Complex (MHC) (also known as the Human Leukocyte Antigen (HLA)) that marks the cells in your body as "you". Anything that the immune system finds that does not have these markings (or that has the wrong markings) is definitely "not you" and is therefore fair game. Encyclopedia Britannica has this to say about the MHC: