I can plant right away? (Meaning I can plant them in June and have vegetables or flowers by summer's end.)

It's a little bit late for planting seeds (by the time they're mature enough to produce veggies, the season will be winding down). I would recommend finding starts at your local nursery (young plants, a little older than seedlings). Zucchini and other summer squash are easy to grow and will reward you with lots of food, and there's nothing quite like a tomato from your garden! Basil is also super easy to grow, as are most herbs. Wander the aisles at your local nursery and see what looks good! Good luck!