Answer: I'd start by reading a comprehensive guide to hobby greenhouses, such as the one found on the following website: http://www.aces.edu/pubs/docs/A/ANR-1153/
It will give you an overall view of how a greenhouse operates and how you can control the environment for the specific plants you'd like to grow. Once you've become familiar with plant requirements and how you can provide optimal growing conditions, you can choose the types of plants that will thrive in the environment you're able to provide.
If your greenhouse is heated, you can grow most anything during the winter months; if it is not heated, you'll be limited as to the types of plants that will winter over. If this is the case, choose cold hardy plants and they should be just fine, as long as you can keep the greenhouse temperature above freezing during the winter months.
Since this is a new hobby for you, why not start out with a few established houseplants? Later you can start seeds for vegetables and for flowering annuals and perennials.
Hope this brief answer helps you get started in your new greenhouse!
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