Plug the SD card (after you turn the phone off, of course) into a full-size adapter, then into a USB adapter (unless your PC or laptop has an SD card slot, then you don't need the USB adapter), and see if you can create and delete files on it. If you can, copy the entire SD card to the PC, then format it, then copy everything back to it. Then put it into the phone and see what happens.
If you can't create or delete files on it in the PC, the card is shot. Depending on the card manufacturer, it may or may not be under warranty. (SanDisk warranties their cheap cards for 5 years, some cards for 10 years and the top of the line cards for a lifetime (yours, not the card's). And they'll replace it if you just go to
SanDisk microSD Tech Support, the live chat at the upper right, and tell them what happened. The cheaper the card, the more difficult it is to get it replaced. Samsung sometimes just sends you another one, but sometimes they make you want to kill someone. And some of the cheap Chinese vendors change name so often that by the time the card gets to you they're already doing business under a different name.
As far as moving apps to the card, the only thing I can tell you is
don't.The way apps are written, only small pieces can be moved, and for each piece there's a link in internal storage. If the piece moved is smaller than a link, you actually
lose space by moving it. (That's why some people complain that after they moved apps to their SD cards, they didn't gain any space.) Put pictures, videos, music, documents,
any files, on the SD card. But not apps. (Aside from the fact that it doesn't save you much space, if any - Android apps have to keep their current state at all times. Android can kill any app at any time. [That's like swapping to disk in a PC, but it's
a lot faster.] That means a lot of writing. An SD card's life is measured in write cycles - it only has a fixed [even if huge] number of them. But if every app moved to the SD card is constantly writing its current state to the card, you can kill the card in months.) So move files to the card, but don't move apps to it. And if you're going to keep so many apps and files, you need a phone with more than 8 or 16GB of internal storage.