Hi and welcome to BP.net!!: I'm very glad you found your way here!
Cassandra really summed everything up very well. If you choose to buy a ball python at one of the big pet-store chains (or even most mom&pop stores) they are likely wild-caught or captive-hatched animals that may have more problems to deal with than a captive-bred baby from a reputable breeder.
It's awesome that you're learning and researching before buying!! I highly recommend getting the enclosure set up first and making sure you've figured out how to maintain proper temps and humidity....then when you finally get your new buddy, they'll have a perfect home all ready to go into.