You have not provided any proper system info or other details, but on a hunch, and let me be frank about it, you haven't bothered to even read the most basic help and neither created a comp nor added a layer to it, hence none of the tools are available. Does that cover it? I'd bet it does. So for what it's worth, your journey starts here:
that's right, i didn't read the help or fill-in the system info. no interest in that. i'm not a film director, and don't pretend to be one. nor am i an adobe junkie. i just wanted to increase the exposure and remove some grain from an amateur video. just like increasing the brightness and reducing contrast on a TV set, i don't expect to have to read through an instruction manual and look up terms like "comp" or "adding a layer"! nor am i interested to view a dozen tutorials just to edit one video.....i'd rather find user-friendly software from a company other than Adobe!
Every piece of software has a learning curve, and its own terminology. After Effects is a complex professional tool, used by home enthusiasts right through to feature film makers.
There's plenty of very user friendly video editing software that will do the tasks you've mentioned easily. Might I suggest Adobe Premiere Elements.
For the record, you can't apply an effect to anything in After Effects until you have selected a target layer in the timeline. This functionality is true of any video editing or compositing software I can think of,