About the interpretation
Notes at the same position are considered parts of a chord. To get independent voicing (for example notes with different stem directions), such as for vocal material, you need to use polyphonic voicing.
If two notes beginning at the same position have different lengths, the longer is displayed as a number of tied notes. To avoid this, you can either use the “No Overlap” feature or polyphonic voicing.
One note is often displayed as two notes with a tie. This is only how the program displays the note, there is still only a single note “stored”.
Generally the program adds ties where necessary (if a note stretches over a beat), but not always. For more “modern” notation of syncopated notes (less ties), you need to use the syncopation feature.
If you want a long note to be displayed as two (or more) tied notes, you can use the Cut Notes tool for this.
If a note has the wrong accidental, this can be changed.
If two notes on the same position are too close to each other or if you want their “graphical order” in the score reversed, you can do this without affecting playback.
Stem direction and length is normally automatic, but you can set it yourself.
If you are scoring for piano and therefore (or for other reasons) need a split staff, there are special techniques for this.