There’s a lot more to understanding and interpreting a Lead Sheet than just reading the notes in the melody…
Let’s take a closer look…
Key Signature
Based on the key signature (no sharps or flats), the fact that we start and end on a C chord, that the melody notes emphasize the notes C, E, and G, that the melody ends on the note C, it is a pretty safe bet that we are in the key of C major.

Of course, we should play and sing out loud to see if our ears agree! It should sound and feel like the note C is resolved and stable.
Time Signature
The time signature is 4/4, indicating that an underlying feeling of four-ness should accompany each measure…

Form & Melody
The form is eight bars long, and the melody is broken into two almost identical 4-bar Phrases. The only difference between the two phrases is the last three notes (more on this in the next lesson)…

Form & Harmony
The C(I) chord establishes the home key and major-ness of the piece and the G7 (V7) chord provides harmonic tension that craves resolution back to the C chord.

This pattern of tension and resolution is an essential element of most musics.