Probably the most common question I get as a ‘photographer’ is ‘which side do I put the buttonhole on?’
Traditionally men wer theirs on the left, women on the right, but if you want to do something different I wont be telling you off.
As for attaching, use a good pin, something with a bit of bling is nice, place the buttonhole to the outside of the suite buttonhole, you got it, it doesn’t go in the hole, even though the name suggests it. Then pin either from the back going through the cloth then the stem of the flower then back to be invisible, or nip the cloth on the outside then the stem then through the cloth again to show off a fancy pin.
Mens flowers face up, women’s often face down, this is mainly todo with the materials used in suites v dresses.
However you wear it, be aware of where the point of the pin is don’t want to stab a small child when picking them up.