For vegetables you do not want to start indoors, you can plant them directly into the garden. As a rule of thumb, plant seeds three times deeper than the seed width. Seeds planted too deeply will not germinate. The garden soil should be wet, but not soggy before you start planting, so water deeply and then wait 15 min to let the water soak into the soil.
Check individual vegetable entries in the Urban Seedling Store for specific information per vegetable on planting depth and spacing.