Today, l was at my local golf course, and on a par 3, l hit the flagstick on my opening shot. What happens when l do this (the ball didnt go in the hole)

If the flag was in the hole it was exciting was not it. no rule
If laying down and someone putting it is different.

First of all great shot. If the ball did not go in the cup you have to play it where it lies after hitting the flagstick.

Done that several times only 2 times it has gone in the hole. No rule.you are hitting your second from where the ball lays on the green

Then you put. You do not get any bonus shots or extra hits. You just play it normal. If l were with you l would have said something very loudly and gave you a high five and said good shot but thats about all you get.

No rule , no penalty for hitting the flag stick on a drive, approach, or chip shot.
2 stroke penalty for hitting the stick with a putt.
any shot that is not struck with a putter can hit the pin. the pin must be removed before the ball is allowed to contact it when using a putter even from the fringe, or the stick is then considered an aid in sinking the putt.
2 stroke penalty.
take note the caddies will remove the flag as the ball approaches the hole during putting.

nothing
as it lies, not a hole in one, no penalty either
it only means something if you hit the flagstick from on the green

although.congrats man, thats one hell of a shot
is there a dent in the flagstick?

you get an extra 40 points in stableford, you get automatic win in match play and you get 30 shots deducted from stoke play. What do you think happens?