Whistle or hum a song, and it will be the melody that you think of. Melody is one of the most pronounced characteristics of any piece of music. It is a series of notes that are played one after another that repeat throughout songs and drive the memorable part into the listener's conscience. Verses and choruses of songs may have different melodies within the same song, but sound good when put together in a cohesive pattern. Even song styles that appear to have no melody, such as rap, may have some sort of hummable pattern that sticks in people's minds.
To modify and support the melody of a song, harmonic tones are introduced. Harmonies may or may not be a melodic series of tones, but they serve to make the melody sound better. In popular music, melodies are introduced first and are usually played at least once with no embellishments and then harmonies are added to create more texture to the song. In a diatonic scale, the most usual harmonic tones that are played with the melody are the third and fifth notes of the scale. In other words, if you are playing a C scale and the note C, the harmonic tones would be the third tone of the scale, the E, and the fifth note of the scale, the G. If you wanted to create a melodramatic or sad mood to the piece, you would flat the third note -- in the scale of C, you would play and E flat.
Tempo refers to the pace of the music. The beat is usually determined by the key signature and the tempo is determined by the beat. Many of the songs of popular music are written in 4/4 time, which means that you count four beats to a measure, and it is the quarter note that gets one beat. Music that has a hastened pace, such as marches, are played in what is called "cut time," which divides the 4/4 music in half to speed it up. Terms that indicate the speed of the tempo are indicated above the staff in the time signature. For example, largo is slow, andante is a walking tempo, allegro is fast, and presto is very fast.
Dynamics is the other element of music that creates character. Music can be played softly (piano) or loudly (forte) or anywhere in between. It can increase in volume (crescendo) or decrease in volume (diminuendo).