Set peat pots in your commercial Jiffy greenhouse product as instructed per the packaging.
Fill pots to rim with a quality seed-starting potting mix. Seed-starting mix is formulated to be extra lightweight to allow for roots to easily grow, usually consisting of compost, peat moss and an agent to help retain water such as perlite.
Plant seeds as instructed on the seed packaging at the recommended time before frost. Always purchase seeds packaged for that growing season by a reputable packager. Follow instructions completely, for best results. Different plants have different planting specifics, including spreading on the soil surface, pushing underground, soaking in warm water overnight, or even scarification -- scratching or cracking the hard shell of some seeds. Only force seeds that are recommended for starting indoors because some plants cannot take transplanting.
Water the seeds by pouring water between the peat pots and allow them to soak it up until moist.
Replace the greenhouse lid. This creates a warm, moist environment similar to the conditions of late spring after frost has passed.
Move greenhouse to a mostly sunny window once seedlings begin to sprout. Keep the lid on as much as possible until seedlings reach the lid's surface. Once the seedlings reach this height, start to allow the pots to dry between watering to force seedlings to grow a strong root system. Turn greenhouse, if needed, to keep seedlings from leaning to reach the sun.
Move seedlings outdoors after the frost has passed, during the day for a few days and then overnight before transplanting. This idea of "hardening off" helps plants deal with the outdoor conditions with less stress.
Transplant seedlings by placing the entire Jiffy pot in the ground, following spacing recommendations. The biodegradable material may already have roots popping through.