eslHQ - “Here we go”?

It has two uses.

1) If you hand something, to somebody, there are several things you can say, including :
Here you are / There you are
Here you go / There you go
Here we are / There we are
Here we go / There we go

For example - in a shop :
A : Can I have one of those big brown teddy bears please?
B : Yes sure. (Hands the customer the TB)Here we go.

2. It means "we're starting!"
For example - a father is teaching his daughter to ride a bike. She's sitting on the bike, but not moving yet. He's holding the back of the bike ready to keep her balanced :
Dad : OK, are you ready?
Girl : Yes!
Dad : OK - here we go!

An extension of this is the football chant - Here we go, here we go, here we go! - which has the idea "we're on our way to winning" - or at least, that's how I've always interpreted it.