Need Help with my Rebel XT settings

I'm new to your threads - and I have read about all the photography language but I can not yet digest it. Could someone please suggest some settings for me to use - I have taken really good photos - but have recently played with my settings and now I don't know what they really should be on most of the time. I love taking portraits - either close up or when they are about 8' away.
I know my ISO is set to 100 - and I think that is okay...I have an external flash accessory and I also use natural light a lot. But I don't know about this 1/200 thing on the left side of my screen...and I don't know about the f.5 or whatever - please forgive my ignorance but I'm curious what settings to use.
THANKS!
I'm looking forward to posting pics that I have taken recently to get some feedback.

There is no one best setting, the function of metering isn't cut and dry, you'll need to do research to find out how to best manipulate each of the metering functions for the specific scene you want to shoot. Its also not something one could briefly cover in a simple forum response either. If you are near a community college, you could check out one of their photography fundamentals course, which should acquaint you with the 3 functions of metering: ISO (sensitivity to light), Shutter speed, and Aperture.

I'll suggest a setting for a full (or near full) moon shot - which is an excellent subject to learn on, and something automation will *not* be able to accomplish. Try f/9 1/800th ISO 200, adjust slightly as needed by checking your histogram and seeing if there is any solid white color on the moon. You do not need a tripod for this (at 1/800th shutter, no tripod is neccesary), and you should turn off your auto-focus and just manually focus to the infinity marker. It can be reasonably viewable on a 200-300mm focal range, but much better at 400mm and beyond if you have it, no less - the point isn't to get a great shot but to learn how to manually set an exposure. The in-camera light meter is useless in getting a properly exposed moon shot, but turn your metering type to 'spot', point your center cursor to the moon, then point it to the night sky, and notice the difference. The experience might help give you an understanding of metering and how it works. I frequently take moon shots when full just for the fun of it, and get that exposure, I'd like a 1000mm lens plus a 2x teleconverter to do it, I might see somebody waving back ;).

Of course, if you only have the kit lens 18-55, thats a pretty useless suggestion.

Thanks for the idea on practicing with the moon. Most of my subjects are much closer :)
I have 3 lenses....the kit and a great zoom lens and a macro. I have gone back to look at some older photos and am trying to look at the details under properties to see what settings I used....guess I'll have to keep practicing until I find the one that worked best. I shoot outside in daylight. Just wish I knew how to change certain settings on the camera...when I'm out shooting, I hate to stop and keep fidgeting with the dials .....I might take 200 pics of one family in 90 minutes. So if I'm doing portrait settings most of the time with one person or a small group - I would imagine I would use the same setting 90% of the time...just need to figure it out I guess.

No, you don't use the same settings 90% of the time, there are differences in each scene and exposure, required shutter differences, f-stop differences, you also may want to adjust the ISO sensitivity to accommodate said differences. For a close up of one person you may want something as wide as f/2, for a more distant shot of a group of people you would want something more like f/6.3, this change will also effect your shutter speed. It is not one setting fits all, and especially when you are outside, the amount of light changes drastically from shot to shot.

The purpose of the moon shot suggestion was not to familiarize you with shooting ultra high contrast subjects late at night at miles away, the point was to help you understand the function of metering. If you don't understand the function of metering, changing your controls is useless. You cant drive a manual stick shift just by throwing it into random gears. Knowing how to change them is only useful if you know why you are changing them and what changing them will do.

By 'great zoom lens' I assume you are speaking of the 75-300mm? Which would suffice for the moon practice. If you want a one-setting-fits-all, your only solution is an automated mode.

Sorry to be blunt, but its really not as easy as you are wanting it to be.

*edit - if you learn the function of aperture, you can use aperture priority mode, which will give you more control than an automated mode. You can start to learn about aperture here - http://en.wikipedia.org/wiki/F-number

I don't want it to be 'easy' so to speak, I just want to learn. I need a person in front of me I guess to show me how to change the Fstop - I don't know if it changes on it's own per picture based on how much zoom you use or what. So far I must be getting away with something because I'm getting paid a few hundred dollars for 90 minutes of work. And so far everyone is very pleased with their pics - even though THEY think the pics are great - (even though I am not changing settings) - In my opinion they could be better if I understood all the things the camera can do.
Thanks for trying to help!

Changing the aperture (F-stop) can be done in manual by pressing the AV +/- button and simultaneously moving the control dial near the shutter release, or, in aperture priority mode, by simply moving the control dial. It does not change on its own, unless triggered by automation. If you have a variable aperture lens, and you are zoomed out with the widest f-stop, then it will adjust on its own to the next maximum f-stop to its zoom. So, if you have the 18-55, and you are at 18 and set it to f/3.5, zoom it to 55 and it will be f/5.6 (because f/3.5 is unavailable at 55mm on that lens). However, if you set it to f/8, it will remain constantly at f/8 regardless of the point in the zoom.

All pics can be better, there is never a point when a picture is an ultimate, un-improvable image.

Thank you so very much Anbesol for trying to help with this!!! I really appreciate it! This seems to be a wonderful place to learn. Years ago I knew of a website and people would post a pic along with the details about what the ISO and Fstop, I think that would help me as well. I agree - all pictures can be better. I know I need to improve and when I see crisp photos with outstanding light I get so jealous and I want to achieve the same thing. I should post some pics on the other threads to get feedback on what I could have done to improve quality. Thank you so so so so much for explaining this Fstop thing to me. Today I'm going out to take some pics of my own kids - don't think I need the zoom lens for that so I'll just use the one it came with. I will fiddle with my settings and see what I get. Thanks again!!!!! :)

Not a problem at all. This place is a great place to learn, if you check out the photo critique board, this forums most active board, post some of your pics and people often have ideas of ways to improve your shots, either compositionally or technically.