Division is a way of answering the question: how many of these things can I fit into that box? If you divide nine by three, that's the same as asking this question: if I have a box that will fit nine things, how many groups of three things will fit in the box?
How to do long division
To do long division, you need to fit one number (the divisor) into the digits of the other number (the dividend) to slowly build the answer (the quotient). This video explains one way to write down what you're doing so you don't lose track, but you can write it down any way that works for you.