"I buy flowers."
My sensei used to say that the o- prefix is there to make the word sound elegant; it doesn't mean anything, but it makes you sound educated or respectable, particularly with oeople you don't kniw well. I would use the o- prefix all the time just to be safe, though you might drop it if you're among close friends (though I don't know if this theory is correct).
i heard it basically means "honorable" and that's why it's fancy and why all the "honorable" jokes and references exist. it's respectful not just as being polite but as showing respect with whatever it's attached to as well. for example when you talk to others about their mom you say okaasan so "your honorable mother".
Same here. Some other sentences do understand 買います but not this one.