Torrenting is simply a special method of uploading and downloading files. I can elaborate if you wish, but I’ll leave it at that. It’s worth noting that torrenting is typically used to distribute illegal media-- there’s nothing wrong with the act of torrenting itself, but because of the method of which torrenting is achieved, it’s mostly used to download/upload pirated movies, games, music, etc. Lots of legitimate things can be torrented, such as Linux distributions. If you’re ever considering torrenting media which may be illegal, make sure you’re fully informed. (Many will argue about the ethics of pirating media, I think this is beyond the scope of this discussion.)
As for metadata, “meta” means “self-referential”. So Meta data is data about data, which is to say, it’s information about itself. Metadata describes many aspects of a file. If you’ve ever opened the properties of a file and seen that it was “created January 1, 1980”, or “1.2 MB”, or “authored by Big Books Inc”, etc, that’s all metadata. In terms of privacy, some files could possibly have metadata such as the name of the user who created it, their geological location, the device the user used to create it, etc. I personally don’t think it’s something to be extremely paranoid over, but it is something worth looking a bit more into if you care about online privacy. Also worth noting that most image sharing sites and services strip images of their metadata when you upload them.