Once your plants are big enough it's time to put them in the ground. For my tomatoes I bury them up to the first set of true leaves. Some plants don't like this so consult the interwebs for proper planting guidlines. It's important that you bury the entire pot, exposed edges might wick the water away from your seedlings. If needed, trim the top edge off or cover with mulch. Don't try to remove the pots, you might have roots growing into them. The pots will decompose and help feed the plant. Happy gardening!