This is very simple way to start your seeds and be ready just when the season starts.
Step 1: Only One: Ready, Set & Go!
Get any kind of pot your plan to use, put potting mix inside, put your seeds, water properly....
Get a piece of plastic wrap big enough to cover your pot, cover your pot and that's all.
I use small yogurt plastic containers as pots. You can see the seedlings growing through the plastic wrap. Once the seedlings are big enough (but still small to transplant) you can open the greenhouse by removing the plastic wrap. This could also be done to water properly.