The most required functions you will find in the left part of the toolbar.
Save (Store current work)
Open "Entering music over graphic keyboard
Real time recording (over Midi-Keyboard)
Playback Start / Stop
,Toggle between full score-mode and single-part (voice) mode
Toggle between separated voices (lines) and merged (unified) voices (lines)
Magnify (Zoom In or Zoom out factor) expressed in per-cents.
, Toggle between print-page-view mode and work-view
Undo - cancel the changes done by last action