I'm not sure I fully understand your question. You want to use an SD card into a Galaxy Discover without an adapter? If so, you can't... The Galaxy Discover supports microSD cards, not SD cards and since the latter is bigger, there's really no adapter that could make it fit into a microSD card slot.
If you what you have is a blank microSD card, then you should be able to use it without issues. Just pop it into the microSD slot and you're good to go (your phone may prompt you to format the card, though).