This is a video on how to format or erase your SD Card (memory card). Warning: Do not do this unless you have backed up all data you want on the memory card as it will be compltely erased.
If you're constantly getting SD card errors in your notification bar, it may be a sign that your SD card has been corrupted. Formatting your SD card usually does the trick to make that annoying error go away for good. However, it does wipe everything off of your memory card (but there's a good chance that this already happened due to the error).