"Why did you take so long for the confession?" "Because I didn't know how to do it."
Jamal has been publicly declaring that he is a fan of Dragon Quest, but recently, he finally confessed that he is a secret admirer of Final Fantasy.
After getting an assistant position in a finance office, she confessed that she is actually bad at math.
You can often associate "good" or "pure" things with the color white. So when you announce something that's white (and pure) it's a confession. You're getting out the evil and making yourself white and pure with your announcement.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.