It would be better to stick with the YaST2 package manager. Explore the available packages and you may find what you need is already available. If you run "kdesu yast2 inst_sources", you can easily install some more SuSE repositories that have non opensource packages for media players, codecs, video drivers, etc. A package you download from the web that isn't for that version of SuSE may use different library versions, causing you to need to locate different packages to install as well. If it is a package for a gnome or kde program, you could end up having to update almost all of KDE or Gnome. So be careful which package you try to install. You would probably not continue in such an extreme case.
To install a downloaded rpm can run:
sudo zypper install <the-full-package-name>
sudo rpm -Uhv <the-full-package-name>
If you downloaded a package and a couple dependencies, you can include all of them as arguments:
sudo zypper install <rpmfile1> <rpmfile2> <rpmfile3>
If you first cd into the directory that contains the package you can press the TAB key to complete the spelling of the package for you.
Clicking on the file in konqueror and then opting to install will also work.
There is a web site http://rpm.pbone.net
that is great for finding a package for a particular distro & version. It can even check your system and indicate which dependencies you need. Go to advanced search and check the box for openSuSE and your version.