How do i grow plants with a small cheap portable green house?

The most important thing is don't put it in direct afternoon sun unless you want to create an oven. It would be best if you could put it in a location with morning sun. Most plants will do well with 4 to 6 hours of sunlight. You have other things to consider, are you only trying to start seedlings? Are you growing flowers, vegetables? What area of the country are you in. You could get help by doing a search for a Master Gardener. All you need to do is type in your state and Master Gardener to find one. They can tell you what will do well in your area of the country.

Even if you live in a cooler climate, you can grow some really nice flowering plants in a little greenhouse. In the afternoon you should open the door for ventilation if it is one of the really small ones with no windows.

Good luck!