Excel is capable of doing almost anything and there are myriad ways it can be useful. The question to ask is how to get people started. Like anything else, it needs to become second nature--an extension of yourself--to be a useful tool. You probably can't envision working without a calculator, but if you had to look up how to use it every time you needed it, you probably wouldn't use it. Excel will be useful when the user can do the basics without thinking about the mechanics. From there, they can explore other features that will make their lives easier.
Start with any basic tutorial or class to get proficient with the fundamentals and a general familiarity with what Excel can do. For features beyond the basics, focus initially...