Amazon S3 + Lambda (Node.JS) clarification on the s3.upload() method

I am following this tutorial wherein the programmer used this code:

await s3
      .upload({ Bucket: bucket, Key: target_filename, Body: file_stream })
      .promise();

Now, I understand that the method above would use the initialized variables file_stream, bucket, and target_filename (which he didn't bother typing out in his tutorial).

But the tutorial is hard to follow since (for what I know) the Key parameter inside the upload is the actual directory of the file to be re-uploaded back to S3.

This is confusing because at the file_stream variable, another Key parameter exists inside the method getObject().

So, is the filename inside the getObject() method should be the same as target_filename of the upload() method? and can you initialize the variables mentioned just to make it clearer for this question? Thank you.