I do not know what. I do not know what the function keys do on my Dell Inspiron 1525. I have 12

Question

I do not know what the function keys do on my Dell Inspiron 1525. I have 12 of them and only three have pictures on them and even that isn't clear as to its meaning. I am afraid to press the Fn key and one of the function keys to see what will happen. Why doesn't something come with each computer to explain how to use the keyboard?