When downloading software it is very important to download from an official site.
If you get the software from the people who make it then you can be sure - as much as you can be sure of anything - that you're getting the "pure" version without adverts/malware/etc. Basically, the people who put so much time and effort into making the software don't want you to have a bad experience with it so they'll give you a nice clean copy.
There are certain exceptions to this "get it from the source" rule - for example, Partha's Place offers some different GIMP packages - but, for the most part, if in doubt get the software from the people who make it. Why bother going to the trouble of getting it from elsewhere?
In the case of Scribus, you should go to https://www.scribus.net/
and follow the links to wherever the site says you can download it from - which is currently SourceForge. (If you want the 64-bit version you may need to look at the list of versions available as your browser might not choose the right one automatically.)
In the case of GhostScript, for Windows and Linux you can get it from http://ghostscript.com/
and follow the links as appropriate. (The version you probably want - unless you have specific needs - is the "Postscript and PDF interpreter/renderer" under the "GNU Affero General Public License".) For Mac you can get it from http://pages.uoregon.edu/koch/
where you just need to choose the latest version.
I hope this has helped. (If everything works okay it would be great if you can say as much here so that people reading this can be more confident in following the same path.)
On the other hand, if you are still unsure of what to do, or have any other problems, please don't hesitate to speak up.