What is the sound of pleasure? What sound puts you at ease? For most people that is some nice music. Just be sure you don't put on any Bieber... that would be like 不音楽 or something... I kid, I kid.
This is a jukugo word, which usually means on'yomi readings from the kanji. You haven't learned this reading for 楽 yet, so here's a mnemonic to help you:
If you play your music too loud, people will come and gawk (がく) at you. But if you try to turn it off and say, "OH I DON'T LIKE MUSIC ANYWAY!" they'll gawk at you even more. Learn proper music etiquette and people won't gawk at you so much, okay?
There will be a big music event tomorrow.
Could you turn up the music volume a little more?
I like the music of Takeuchi Mariya and Yamashita Tatsurō.