I have heard the phrase "Here we go" a couple of times. And some other time I hear "There we go". What do they mean and what is the difference of the two phrases? I somehow feel it could be replaced by saying "Let's go", could it be?
here we go is more commonly used to indicate the beginning of something.
there we go is more commonly used to indicate the completion of something.
here we go can be used when going somewhere.
Here we go on another adventure to the movies!
Here we go can also be used more negatively, almost sarcastically.
"You don't want to travel for the holidays because you don't like my mother!"
"Oh, here we go! I don't dislike you mother, their guest room just smells funny."
In the above scenario, the second speaker believes a dispute is about to unfold, which is rudely indicated by their saying
here we go.
there we go, we commonly see it at the conclusion of an action. For instance:
Grandpa was very old, and had bad knees. It was difficult for him to sit on our low couch. i heard him strain with effort as he sat. "There we go" he said, with a sigh, as he finally settled onto the squishy pillows. "They don't make them like they used to."
There we go can also be used to express approval. For instance, if you're teaching a child to ride a bicycle, when they do a good job, you could say, "There we go!" In this situation, you could also use "There you go!" However i think because the activity is together, either is appropriate.
Similarly, it could express approval of more removed events. For instance, your football team scores on TV, and you exclaim, "There we go!"
There may be other uses of these phrases, but I consider these the main ways to use them, which are actually fairly distinct, I think.
You also mentioned
let's go. I think that can be used mainly to indicate that it is time to go. For instance:
"Is this a good time to go to dinner?"
"Yeah, let's go!"
It can also occasionally be used as encouragement.
For instance, as a sporting event, you can express support for your team, the Cubbies, by shouting "Let's go Cubbies!"
The use of "here/there we go" represents various emotions, although I mostly hear it as an expression of mild annoyance by some [possibly expected] event or circumstance. The meaning is essentially "look, just as expected/anticipated, we are now witnessing it". The other end of the spectrum has a similar connotation, except it's a positive resolution of something expected/ anticipated, thus an expression of gladness something is finally occurring/happening.
The difference between "here" and "there" is, as you might imagine, governed by the proximity of the action. If whatever is happening/occurring touches the speaker directly and immediately, "here" would be used. If the happening is somewhat distant, even just perceived as such, then "there" is used. Also, the speaker can use "there" in an attempt to distance themselves from the event.
No, "let's go" is not directly related, as I understand it.