I want information in one column to be used in a formula to insert in another column for each row. E.g. - Column AA is used in a formula in column U. The rows will all use the same formula. How do I do that without having to type the formula in for each row "=(number/number)AA3" in cell U3 and so forth?

Unless I'm misunderstanding the question, just grab the fill handle at the lower right corner of the cell in the top row with your cursor and drag it down. ( Select the cell in the top row that has the formula, move the cursor to the lower right corner of the cell, until it turns to a "+" sign, click and drag down.)