I plant several seeds in a little peat pellet greenhouse like this one:
Once they've germinated, I let them grow a bit more in the greenhouse (until the leaves start to touch the lid) and then I move the pellets into empty flower flats that I've saved. Like these (minus the marigolds, of course):
I just keep the pellets litghtly watered but not soggy until the plants are about 4-5" tall. Then I plant them out in pots, but it should work the same for planting them in the ground.
I've been planting a new set of beans about every two weeks so I will have them throughout the season. You should have plenty of time to get a good crop!