gambling is not a way to earn bitcoin online and even if you can earn something out of pure luck it is definitely not an stable way to earn bitcoin.
for more reliable way you have to do some jobs based on your skills. trading is one of these ways which requires some skills which everybody can learn.
Gambling will always be a good method it you have too many coins and you want to get rid of some of them.
The house always wins.
Skills are really better. But where can I learn those skills?
you are right, gambling cannot make you good money it can only take it from you and in my opinion you should never do it if you dont want to lose money