There are three ways of installing software in SUSE.
1. YaST, using YaST sources to pull the RPMs down automatically. The easiest way. If you can do this, do it. Just add the sources listed in the following sticky, using the instructions. Take care to add the Packman source - it contains lots of useful software.
2. YaST, by downloading the RPM manually and clicking on it in Konqueror. (I can't get the YaST to see /rpm as a source, for some reason.) This is the best way for packages not contained in the YaST sources. When you get dependency problems which YaST can't solve using its sources, download the needed RPMs yourself (Google them or go to rpmfind.net and make sure they match your SUSE version). Install them using the same method, and then continue. This way everything gets entered into the RPM database.
3. Using tarballs. The hard way, involving compiling and unhelpful error messages, as well as the usual dependencies. Usually only necessary if you want obscure programs or the very latest releases.