Hi Donnadee and welcome to GoY - I guess you got your wee greenhouse for Christmas? Tempting as it is to start seeds NOW you will do better to hold off for a couple of months. Are you wanting to propagate flowers or veggie seedlings in it?

I use mine for small perennial plug plants which I want to store over winter. They get protection and can be planted in the spring. i have also put bulbs and coums in there. I have oxalis triangularis growing happily, plus some hardy orchids

You can also raise all sorts of woody cuttings this time of year, if your not into veggies and flowers

I know people say don't start seeds yet as it's far too early, but buy a reasonably good heated propagator and put that in your greenhouse.
You'll need to make sure it is shaded and/or the lid removed on sunny days otherwise your seedlings will cook.
But with this combination you should be able to raise lots of seedlings very early in the year, which will save you lots of money in buying plants.
I get most of my seeds started in damp vermiculite in little yoghurt pots covered in cling film. As soon as things germinate and are large enough to handle, prick them on carefully into normal compost in pots.

If it is a stand alone plastic greenhouse over a frame, then I would dedicate the bottom shelf to bricks to ensure it doesn't blow over. I hear stories of people's stand alone greenhouses full of plants blowing over in strong winds and losing all of the plants inside. Lean it up against a fence/wall and line bricks along the bottom shelf and you should be fine

Yep i did get it for xmas lol so excited about growing my own veg, thanks for all your useful answers