Hello Korash!

The "_rer" is just stuck to the name to diferenciate the input file and the output file, there was an error in the naming in step 4 I was using mosaico_re.tif instead of mosaico.tif, I've edited the post and hope it is clearer now.

I usually run the commands in the same directory where the image files are, so there is no need for incluiding the entire path to the file when you run the command.

Hope this helps!