Definition of the Derivative help

I have no idea what a DERIVATIVE is. I'm being asked to "find the definition of the derivative".
They give me F(X)=#
Do I find F'(X)=#?

How?

Can you do some examples like
F(X)=-5 to find F'(X)?

and

F(X)=3x-7 to find F'(X)?

and

F(X)=2-3x^2 to find F'(X)
Then F'(1), then F'(2), then F'(3)

and

F(X)=5x/3+x to find F'(X)

I know the answers. The answers aren't important. I just want to know the steps in doing it. I'm really terrible in Math and I am completely lost. Please help! Explain it like I'm 5. Thank you.

I'll do the middle two and leave the outer two probelms for you to try. The definition of the derivative may be expressed as
lim [ f(x+h) - f(x)]/h as h goes to 0
So, in writing the calculation of the deriviate I'll write "lim" which implies I'm writing the limit as h approaches 0.
2. f(x) = 3x - 7 and f'(x) = ?
lim [ 3(x+h) - 7 - (3x-7)] / h = lim [ 3x + 3h - 7 - 3x + 7] / h
= lim [ 3h] / h
= lim 3
= 3
3. f(x) = 2 - 3 x^2 and f'(x) = ?
lim [ (2 - 3 (x+h)^2) - (2 - 3x^2) ] / h = lim [ 2 - 3 (x^2 + 2xh + h^2) - 2 + 3x^2] / h
= lim [2 - 3x^2 - 6xh - 3h^2 - 2 + 3x^2] / h
= lim [ - 6xh - 3h^2] / h
= lim [ h ( -6x - 3h)] / h
= lim [-6x - 3h]
= -6x
Since f'(x) = -6x, you may find the values of f'(1) = -6(1) = -6, f'(2) = -12, f'(3) = -18.