ISO is your camera sensor's sensitivity to light. A lower number means a lower sensitivity, and higher number means a higher sensitivity. 100 is standard and "normal", but terrible for low-light situations, as the sensor is not very sensitive to light and won't pick out the variations in a dark room.

Note too that higher numbers have more noise, as the higher sensitivity comes at the expense of sharpness. So a lower number will be sharper, but needs more light, and vice versa.

In point-and-shoots or for people not using any manual settings, I suggest leaving it on auto.

AF lock is auto-focus lock, and this happens automatically on all digital cameras when you push down the shutter button. However the button with this label also comes in handy if you are shooting a moving scene and want to freeze an action in a blurry background, as you track the subject. You can hold it down and freeze your focus at that exact length and distance. It's handy, but I don't think I've ever used it.

AE lock is exposure lock, it lets you lock the exposure settings in for multiple shots instead of the camera changing them in between. You'd want to use this if you're shooting a lot of photos at once, or if you're shooting something for a panorama, or if you're shooting things in sequence, really.

FE lock is flash lock and since you'll probably never change your flash settings (most people don't), and since the on-camera flashes are all so terrible and should be avoided like the PLAGUE, you will probably never use this ever. I haven't, and most pros I've talked to haven't either (of course, most of us use off-camera flashes we bought extra, too.)

*drools*