Where does one get first plants? Perhaps a friend given you a plant. May be you have seen them in a local nursery. However you get them, you need to know their names and their needs. One should never buy an unnamed plant unless it is a species and you think you can figure at least what genera it is. Then you can bloom it and refer to botanical descriptions or expert to find its full name.
Unnamed hybrids are virtually valueless, unnamed plants can not be shown and half the fun of growing orchids is learning about their origins and genealogy.
Keep in mind your conditions when buying your first plants. Until you have really accumulated lots of experience in growing orchids, you should not try plants whose needs you can't meet.
Many modern hybrids are so complex that these plants less fussy about temperatures. Modern hybridizers have "warmed up" many cool growing orchids by breeding them with species from warmer areas. For example miniature Cymbidiums are intermediate while standard one's cool growing.
If you have joined your local Orchid Society, you will have immediate access to good plants. Most growers have divisions to give or sell. Try not to invest in an awarded plant until you know you can handle it, however do try to get plants in good growing condition. Seedlings and back bulbs are not for a beginner - they may be years from blooming.
Some of the members of your local society will be commercial growers. Make an appointment to see them, be ready to listen and learn, and ask for their recommendations. You can ask to visit some member's greenhouses - every greenhouse is different, but there is something to learn everywhere. When you get there, try not to look at plants only. Look at benches, the heating, shading, watering, hoses, etc... See how plants are arranged. Not everything you see will apply to your own conditions, but keep an open mind. Make notes or sketches and ask questions.
Another good advise for a beginner - don't load up only one genus. Try different orchids if your growing conditions are intermediate. Sticking to just cattleyas or just cymbidiums makes a dull collection and a look of sameness. Most people don't realize how different orchid blooms can be.
However you get your first plants, through friends, commercial growers, ads, catalogues or auctions, try to buy plants that give you flowers at all seasons of the year.
Some Cattleyas bloom more than once a year. Some bloom in season. Most Phalaenopsis bloom in spring. Cymbidiums start in autumn and go on through spring. Catalogues will tell you if an orchid is early, middle or late flowering. Find out about expected bloom period of plants, trying not to buy three of four purple Cattleyas all blooming in autumn.
Often you will find "combination offering" at reduced prices and these are good deals for a beginner to try to grow different species and to see the magic of orchids.
(Photo from Australian Orchids Council screensaver)