The simplest and fastest way to get your sheet music into SeeScore is to use PlayScore 2 for iOS and Android (available on the App Store and Google Play Store). This allows you to take a photo of a page of music with your phone or tablet and to convert it to MusicXML in seconds for import into SeeScore.
Almost all score writing software, such as Finale, Sibelius, FORTE or MuseScore, can export MusicXML scores to be used with SeeScore. It is important to use the most up to date version of the software as MusicXML support is under active development and improving all the time
MakeMusic provides a wealth of information about the MusicXML format including a list of websites where you can get scores. Unfortunately many scores in the public domain have errors which in the worst case means that they will not display in SeeScore. However there should be a useful error message which may enable you to make simple corrections to the file using a text editor. You should report these errors to the site where the file came from or the owner of the software which wrote the file.
Please report any problems with SeeScore to us at Dolphin Computing