Look for files named README.txt , README.md , Instructions.pdf , or similar. This is where the creator usually explains what the files are for.
Often stands for Build, Blueprints, Data, or a project codename. BD-Y-SB-2-3x.7z
If prompted, the creator of the file must provide the password. If you can tell me: Where did you download this file from? Look for files named README
I can provide more specific instructions on how to use the contents. Look for files named README.txt