Cbz (Or cbr, it’s the same thing) files are comic book reader files. These are renamed .zip or .rar files that can be read by a program that makes on screen reading of comics easy and convenient. You can Please Login or Register to see the link. in order to read the comics.
If you DON’T want to download or install the program, then you can rename the file extension (All cbz files are actually rar or zip files) and open them with winzip, winrar or whichever program you prefer (7zip, ultimatezip, etc.) in fact you can probably open them directly without renaming and they will still be recognized.