We often use these phrases in a similar way to how French-speakers use 'Voila!' When you hand something to someone you can say 'Here you go' or 'There you go'. We can use the phrases to indicate the start of something. For example, you are struggling to get a DVD to play properly, and then when it finally works, might say 'Ah, there we go! (or 'Here we go!') meaning 'That's it! Now we watch the film'.

I can't believe you spilled juice on you shirt for the third time. Here we go again. Take off your shirt and I'll wash it, one more time.