In a general way we all instinctively recognize pitch differences because they are built right into our anatomy. Psychologists have studied the way babies particularly respond to the more high-pitched voices of their mothers. Strictly speaking, pitch is a function of frequency. One complete vibration is called a cycle. In music pitches are specifically labelled, from the lowest to the highest.
Tunes are often simple, catchy melodies, like folksongs.
A theme is usually the subject of a work of music. A motive is a fragmentary idea. In music motives are used as a kernel from which a larger work is built. Think of a scale as the pool of notes that a composer uses to write his or her piece. Most cultures employ a scale as the basis for their music, and there are many varieties of scales to choose from.