Help with homework?

i am not cheating like some people do. i dont want answers for a homework ignment i just need something explained to me. i was sick for 3 days this week and didnt understand anything that was being taught in my science cl and i just found out that i have a test coming up on it so i just realy need help. we are learning about simple machines. and i dont understand what each simple machine is..i need incline plane, wedge, screw, lever, pulley, and wheel and axel explained to me please. i just need a defintition of what they are. i tried to read the chapter but its to confusing. anything that explained what each is, what it does, and how it works would be alot of help. thank you so much.