Image sizing for the Web?

Arrgh! I'm so frustrated! My aim is to learn HTML, and I am learning
slowly, but image quality keeps getting in my way. I could really use some
advice.

How do I use Photoshop to make jpegs and gifs smaller in size (Image Size)
without sacrificing quality? I use the Sharpen filter after resizing, but
they still seem much too blurry. Is there a trick I'm unaware of? Am I
doing something wrong?

Any advice will be greatly appreciated!

Thanks, 

Allie Hartman 

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