I did the same thing last year. I used Albertsons as my supplier. I didn't know what to do with the bulbs either, but I broke them into individual cloves and planted them before the end of August.
I harvested them in June of this year and this was my harvest.
I feel like I got a good harvest and it was totally by accident.
The onions I know a little more about. I would guess the variety you bought in a bundle will require separation from the bundle. Plant them two or three inches apart. If you simply want green onions, plant them more than 1/2" deep. If you want to leave them long enough to grow decent sized bulbs, plant them between 1/4" and 1/2" deep.
I planted a lot of onions about one month ago. I've never tried growing them in the fall but always have a good spring harvest. The onions I planted last month are almost ready to start harvesting as green onions or scallions. I will leave most to harvest later in the fall as bulb onions.
I will plant onions again in January for a spring/early summer harvest.