Analyzing data in Excel is one of its great features and there are a number of tools for doing this, aside from sometimes just changing a value and seeing what happens. If you have done this then there is an easier way. This works really well if you have one or two values you need to change.
Lets say you have a formula or function for calculating repayments on a loan and you want to see what would happen if the interest rate changed or the term that you were paying it over changed, then a one input data table could be used to display your options. You could use a two input data table if you want to see what would happen changing both.
Here are two tutorials for each of these different types of data tables.
One Input Data Table
Two Input Data Table