Aha!

"Aha" is something we say when we suddenly find something, or understand a complicated idea, after a lot of difficulty and time.

Aha! I found it. I had been spelling it wrong.

Aha! You have a new boyfriend, don’t you!

Or imagine that your friend told you last week that she has some good news for you. When you meet her, she tells you that she’s having a baby. You say:

Aha! I knew it!

here we go

Say this when you find something you were looking for. It can be a piece of information, or a physical object. 

Here we go. It was in the wrong folder.

(When checking a website to find out when a concert starts:)

Here we go. It starts at seven.

You can also say "Here we go!" when something big and intense is about to start. In this case, the intonation is a little different, with extra stress on “go.” You could say this right before you ride down a big hill on a bicycle, or before you start to play a song with your band.