That's because you're a new member, and new members need to have their posts approved by a mod/admin before they can be seen by the general public. It's a feature of phpbb 3 intended to reduce the spam everyone sees from spambots (among other things).
It's a one time thing. Once you get one post approved you don't have to worry about it again.
When you made these posts, you should've gotten a splash screen saying "your post needs to be approved by a moderator" or something to that effect.
I'll go and approve one of the two topics you made in general music.