I am writing this for my own personal reference, 98% of my photos are still pure suckage so please disregard any advice from me. Warning: this post contains rambling.
RAW mode: Please shoot in this mode, your photos will thank you for it. RAW mode means you see the image as the camera's image sensor "saw" it with no compression or processing. Photos are sharper and colours are crisper. Shooting in RAW also means that you can custom edit the settings your photo was taken with. Yes, shooting in RAW means you will have to manually process the photo before you can upload it but such is the price for quality. Most cameras nowadays come bundled with software which allows you to process RAW photos so there's no excuse not to shoot in RAW. Word of warning, buy a bigger memory card, a 32GB at the very least.
ISO: How your camera responds to light. The higher the ISO number, the more your camera is responsive to light. If you're shooting indoors or under dim lighting, crank up the ISO, if you shooting outside on a sunny day, keep ISO low. Remember, the higher the ISO, the grainier/noisier your photo, so unless you're trying to be artsy fartsy, keep the ISO as low as possible.
Aperture: The opening on your lens that lets in light. This is measured as a "f-stop". This is going to sound stupid, but the bigger the aperture, the smaller the f-stop, and the smaller the aperture, the bigger the f-stop. There's all sorts of nonsensical mathematics involved to calculate this but just remember, the smaller the f-stop, the smaller the field of focus, the bigger the f-stop, the bigger the field of focus. If you want to bring focus to a single flower in a field, choose the smallest f-stop available on your camera. If you want to take landscape photos where you want everything in focus, choose the biggest f-stop available. A word of warning, a small aperture (big f-stop, more in focus) requires lots of light, if there's not enough light, the shutter speed will be longer and you'll end up with blurry photos. If you're working under low lighting but want more in focus, you'll need a tripod.
Shutter Speed: How long the shutter of your camera remains open. Shutter speed is measured in seconds, so 1/1000s is short and 1s is long. The longer the shutter speed, the more light you let in, the shorter your shutter speed, the less light you let in. Long shutter speeds will capture movement, and short shutter speeds freeze action. This means if you need to take a photo of a fast moving subject without blurring - use short shutter speed, and if you want to take photos of dreamy waterfalls, fireworks and light trails - use a long shutter speed. Remember, depending on how steady your hands are, you shouldn't go any slower than say 1/30s or you run the risk of blurry photos. Your shutter speed can also be set to BULB. This setting allows you to manually control when the shutter closes, you'll probably have no use for this unless you intend to do extremely long exposures.
WB: White balance. Exactly what its name suggests, your camera can compensate with more cool (blue) light if you're shooting in direct sunlight to cancel out some of the yellowness or add more warmth (yellow) if you're shooting in a cloudy or shady environment. You can either go full auto (Canons leans slightly bluer) or pick a pre-set choice such as: Daylight, Shade, Cloudy etc. I tend to ignore this and leave it on auto as I usually change the WB when I process the RAW image anyways.
Exposure Compensation: My Canon displays this as a +/-meter at the bottom of the LCD display. Use this to lighten or darken your photo as needed. Useful if you're outdoors and your ISO is already on the lowest possible setting and your photos are still over exposed. Equally useful indoors if you need a brighter exposure.
Auto mode: Please for the love of all the various gods, do not shoot in this mode. This goes for all the other pre-set modes too e.g. Sports, Portrait, Landscape, Macro etc. All DOF is lost in this mode and the flash has an annoying habit of popping up. Just don't. I threw myself head first into AV and TV mode the first week I got my camera. If I can do it, anyone can!
P mode: You select ISO and the camera will select aperture and shutter speed. Good place to start learning without being overwhelmed. I personally don't find much use for this mode anymore though.
TV mode: You select ISO and Shutter Speed, and the camera selects Aperture. Good for indoor/low lighting situations, a high ISO and fast shutter speed ensures that photos stay sharp. You cannot control DOF in this mode. The brighter the lighting, the smaller your aperture will be and thus the more you'll get in focus. The lower your lighting, the bigger your aperture will be and the less you'll get in focus. If you're a camwhore, this is the mode you'll want to use as the fast shutter speed ensures that the shakiness of your hand won't result in a blurry photo.
AV mode: You select ISO and Aperture, the camera selects shutter speed. Good for outdoor/well lighted situations. Remember the smaller the aperture, the higher the ISO/the more light you'll need. I use this if I'm being anal about DOF, but if you use this indoors, you WILL need a tripod.
M mode: Manual mode. You have complete control over every single setting. I like using this when I have all the time in the world to fiddle or when I'm taking photos of things like Christmas lights or fireworks.
Next in this series: Lenses and what all those bloody numbers mean.