I read in the manual that you have to unmount the card first. What happens to the apps that install files to it, or how do I know which apps did? Does unmounting it uninstall the apps or something? How can I view the temp or whatever files that are on it?
Unmounting the SD card makes your card inaccessible; this will allow you to safely remove the SD card without causing any damage to the files installed. This will not do anything to the apps already installed in your SD card; you can follow this tutorial to see the applications installed in your sd card http://support.sprint.com/support/tutorial/View_Installed_Applications_LG_Marquee/26292-1168
Sprint Social Media Care Team
I know that didn't need the tutorial. But it's showing that there is used space on the card. I would like to get a bigger card, so are those files from apps or something? It doesn't show anything on the card when you go to manage apps.
sometimes an app will store settings or backups, or cache info to your card. if you want to view the files and your phone doesn't already have a file viewer app preloaded on the phone, download Astro file viewer from the app market. That will let you look at the External SD card and whats on it...as well as the internal memory.