There will not always be an RPM
for the software package you are trying to install. The software may be very new or not widely used. New SUSE users will not be able to install this software with YaST
; this means keeping track of this software will be more difficult, but not impossible.
Even if no RPM is available, you will often be able to find software in various archived formats that you can use. Some of these packages may include an installer which, when executed, will automatically put all the software's files in the right place. Sometimes you'll only need to extract the software and you can run it like that.
If you're feeling adventurous, you can compile it from source and either
make install it, or build a simple RPM.
I strongly discourage new SUSE users from using these methods unless you absolutely have to. It can quickly make software management very difficult.
You'll need to seek documentation from the software's author to find out the best way to install their software. Usually some Google searching will reveal steps to install this software.