Excel is the standard program to use when working with spreadsheets. This is generally considered the industry standard as it's the most common platform to be using when working with spreadsheets. Still to this day it has more advanced features in it compared to other spreadsheet software. If you are learning any of them, this is the one to master. There are some things to keep in mind when learning this software.
First of all, you will need to get a copy of Microsoft Office. This can be done by purchasing it at the store, upgrading it on your current machine, or even getting the 2010 free ad supported version of this program coming out soon. These will give you the tools to be able to start learning. You can also use open source versions of spreadsheet programs as many of the basic functions and formulas are still going to be exactly the same.
Search online looking for tutorials. There are so many that are free online that will give you the basic knowledge about how to use the program as well as some basic formulas for you to start using. These guides are pretty extensive giving you much of the knowledge you need to know.
Practice learning more of the basic formulas. These are important because this is the basis of the advanced techniques that this program has versus just putting in text into the fields.
Download some templates and start playing with the numbers. You will be able to see the formulas in these and be able to figure out how they were done. This will help you get to the point of tweaking the data and making your own templates.
Go get Excel books. There are many written by third parties that will go into details of advanced strategies. Many of these are very high quality giving you new insights on learning the program properly.
Excel is one of the leading industry standards for spreadsheets. It's a program that can get pretty advanced meaning that there is quite a bit to learn. Find out what you need to do to learn this properly.