The official, up-to-date support info is posted at https://musescore.org/support, visit that page and read it first.
In addition to tutorial material promoted inside Musescore, MuseGroup, the managing company of the MuseScore project maintains an online server https://musescore.org for the musician community free of charge. The community volunteers to maintain written handbooks and a collection of help pages collaboratively. To ask for help, use https://musescore.org/en/forum
Everyone are invited to join the community and encouraged to contribute, see https://musescore.org/en/donate and https://musescore.org/en/contribute . Report bugs of Musescore 4 the windows, macOS and linux software at https://github.com/musescore/MuseScore/issues
There are other really good quality third party tutorial materials, video streams and communities for different level of Musescore users online.
Go to https://musescore.org/en/forum to read news and participate in discussions.
Go to https://github.com/musescore/MuseScore/issues to post and track issues.
The project is available at https://github.com/musescore/MuseScore .
There are other really good quality third party tutorial materials, video streams and communities for different level of Musescore users online, most notably https://school.masteringmusescore.com/ created by Mr. Marc Sabatella. While Marc Sabatella has been contributing heavily to MuseScore codebase and official tutorial materials and diligently helping the community for an extended period of time, that site is not affiliated with Muse Group or any of its subsidiary companies.