Editing scores

General
    space  stop/start
    goto start:  CTRL+SHIFT+left
    goto end:  CTRL+SHIFT+right

Menu Edit > Score Edition Mode
Set signature with Composition > Time Signature and Composition > Key Signature
Then add notes.
Remove note:  RMB on note, Beat > Delete...  (sometimes Beat > Clean...?)
OR select the note (in Selection mode) then DEL key.
Clicking menu bar items applies effect to "current" note.
To de-select current note, click in bg maybe?