They are updates to packages you already have installed on your computer, not new stuff. Since ubuntu is not a "rolling release" distribution, you only get minor security patches/bug fixes, not big version leaps that will change the functionality of your computer.
I generally advise to install all available updates. If you are curious for more details on an update, search for the package at http://packages.ubuntu.com
and read the description and changelog.
Unfortunately from time to time, an update does unexpectedly cause problems. When this happens, you are probably not the only person it's happening to, and you can find help at: http://ubuntuforums.org