Windows 7: Sharing with others on same computer

I got windows 7 about 5 months ago and this sharing thins is about to make me want to find a good XP computer. When I first set it up I couldn't access but few of my files. I have read all I can find as well ask questions on forums. I have finally got it where I can most of the time see my own files. THEN yesterday I downloaded a jpg file from my cell phone to the computer. The image is side ways so I went to rotate it clockwise and the computer says I don't have permission to this file. I messed with it 30 minutes and could never get where I can edit it. Now, mind you it is in a folder and other files in that folder I can edit. I finally deceided to try to save as in another folder, guess what?? It let me do that and from there I could rotate it. This makes no sense to me. How can I make all the files on this dang computer be available to me or anyone who is on my computer? Who ever made this sharing thing this way must be paranoid and trying to hide something from his wife. My life is an open book whoever is smart enough to get in my computer can surely see all my files anyway. All this is doing is keeping me from my own files. HELP HELP PLEASE

Are logging on as an adminstrator? And if so, where are you saving files to (the files you're having problems with)?

Not logged on as Admin. unless it does that when I start the computer. The file that gave me trouble today is in documents/my pictures. This file, when click on share with, has a logo of a locked lock and nobody. I have tried everything to remove that. However it also has homegroup read and homegroup read/write. Tell me of a simple way to go around all this share with stuff