I often hear the word "coming" in many scenes of movie dialogue. Can you elaborate on it? thank you

Generally used to mean to start an activity at once. I used to travel all over the United States. I remember an episode in which a reporter went to the American countryside to investigate and a woman was about to start singing. She started like this-"1,2, 3, here we go" and began to sing.

I was chatting with a net friend, and she asked me to send her a file. She said give me five minutes to find the file, and then she said, here you are. -Start looking.

The following is the explanation in Longman dictionary.

Use when you start to do something or something starts to happen.

Example: OK, let's get started. The game is on.