For Christmas I received a Canon PowerShot S5IS. Two of the available accessories are a Teleconverter Lens and a 58mm Close-up Lens. Could anyone explain to me in layman's terms what these would do for me? Thanks for the help!

The teleconverter will multiply whatever zoom capability by 2 or so. close up lenses come in several flavors. These you attach to the front and they affect your minimum focusing distance, allowing you to get close-ups or macros. For any of these you will need a barrel adapter that converts the smaller diameter of the camera body(typical for a fixed lens camera) to the threading needed for the filter. These are pretty cheap, its the teleconverters that are expensive. You cn also find wide angle lenses too. I put one of these on my Kodak. They are about $100 and give you about 50% more in each photo. If you get the barrel adapter you will be able to get all sorts of other filters too; UV, polarizer, color filters, the possibilities are pretty endless. Make sure you order the right sizes for your barrel adapter!
Beach Camera has a wide variety of this stuff. I got my wide angle there. They have good prices and fast shipping. (I don't work for them, they've just made me a very happy customer!)
Hope that helps!

Since the S5IS has macro capabilities, I'm not sure why you'd need a "close-up" accessory. As for the teleconverter, something to keep in mind.. you already have a 12X zoom that reaches a 400mm equivelent. If you buy it, might want to take some sample shots to make sure it doesn't affect the picture quality.

The folks at dpreview.com do a pretty good job of explaining your camera. If you'd like to have a look, the review can be found here

PS.. congrats on the gift..enjoy :o)

Thank you both so much, very helpful! I really appreciate it :)

My pleasure. Go forth and shoot, and post upon your return :o)