Chords with notes of different length

In the treble clef line (or bass) I want to write simultaneous notes (intervals and chords) with notes of different length. For example, on beat 1 I want a quarter note C and and an eight note E (followed by something to fill that line). Whenever I try to add a note of a different length, it changes the other note on the line. Writing on the other line is insufficient as the notes of different length may sometimes be played by the same hand, and in many cases may be more readable. See the screenshot with examples circled. How do I do this?