The VHS tape is the old school version of a USB stick, only it can store a heck of a lot less on it. Usually, only a 120 minutes which is usually just a recorded movie.
The little tab on a VHS tape was a safety seal to make sure no one recorded over your favourite movie or tv shows. Once you had finished recording on the VHS tape peeling off the little tab would mean that no one could accidentally rerecord over the VHS tape.
If you decided that you wanted to erase the tape again a little piece of sticky tape over the hollow square where the tab once lived would make the VHS tape good as new.