What do you use to reconize a the notes melody.?

like if you have a melody what do you use to build it. Would you reconize it by the notes them selves or intervals in a key or mode like you recoize or use to find it sounds like Major 2nd ,Perfect 5th, major third in the key G Major or reconize. Or be scale degrees like tonic and mediant or notes in a arrpegio in a chord progression. .Im kind of confused about what I use to play by ear or compose