Some time ago I did a tutorial on VLOOKUP and have finally got around to doing one on the HLOOKUP function. It is very similar except that the data is in columns as opposed to rows as you would find when using VLOOKUP.
HLOOKUP will take a value and find a match for it in a table and return the given corresponding value in one of the rows below it. This is useful for finding matching data or for finding a value based on a range. In this example I use it to find staff information based on a staff ID number. However, you can do far more including using it find a value within a range.
You can see a different type of example using student exam results and returning a grade in my VLOOKUP tutorial. Whatever you can do with a VLOOKUP you can do with an HLOOKUP, the difference is the way you have laid the table out. The advantage of a VLOOKUP is that the data is in rows and Excel has a lot more rows than columns, so if you have a lot of data you may want to consider the VLOOKUP.
Here is the HLOOKUP tutorial.