Latest questions about "hidden files"

Once I reset my phone due to slow performance. But I forgot to unhide my folders which were hidden through a File Hide Expert app.

Where do hidden files come from? I have a bunch of hidden files and I didn't hide them. How did they get there?

I had to reinstall the program because I could'n opened my Yo-safe partition. Now, I can open the partition but I can't access my data.

I downloaded Folder Lock and the trial version expired. I uninstalled the program but I still can't see my files in the F: drive.

I have a LG Optimus with Android Gingerbread. I've bought a SD card, which works fine, but my phone says I'm running low on memory.