When a song consists of notes from a particular scale, it is said to be written in the key which has the same name as that scale. For example, if a song contains mostly notes from the C major scale, it is said to be in the key of C major. Nearly all the songs you have studied so far have been in the key of C.
On the recording there are three beats to introduce this song.
On the recording there are five beats to introduce this song.