The Human Resources dept. is a group of corporate-minded employees not unlike the guidance counselors at grade school. Their primary objective is to resolve conflict or suppress complications in the workplace. Break the name down.
"Human." Easy enough. You're human, I'm human. It just regarding people.
"Resources." To a business, this can be anything. Resources are necessary components of a system. Water is a resource to living animals, as you'll recall from science class. Trees and wood are a resource for construction and building. Workers (typically human) are resources for business. Without workers business isn't accomplished.
If you really need a mental image, I'd choose the wood analogy. Picture forests of people and lumberjacks in suits? That's the best image I got for you, sorry.
My best advice is to be on the good side of human resource workers. They are the go-betweens for all businesses to the corporate office. They're kind of like Internal Affairs are for a police department. They have connections and can be very helpful. These are the guys who did your background check and will review you from time-to-time. Keep them abreast of how you feel you are doing in the workplace, these guys love being kept in the loop.
These are also the people you go to with complaints over inappropriate office antics or disputes that could get you fired. If you ever thought, "this isn't my job..." or "you can't just change my hours without asking..." these are the kinds of concerns you bring to HR. Also harassment claims or simple questions about what is or isn't allowed in the workplace go here.
Simple job experience.