This Help Center is about using MuseScore.com. In case you have any questions about the MuseScore software, you need to search the MuseScore.org Handbook or the How to articles. Also on MuseScore.org there are forums, where experienced MuseScore users will often answer your question within just minutes.
If the whole MuseScore/MuseScore.org/MuseScore.com thing is confusing you, see What is MuseScore?