A scale is an organized sequence of notes chosen from the 12 notes in a particular pattern, which gives it a characteristic feel, perhaps a happy, sad, exotic, oriental, enigmatic, or rebellious feel. A scale can start on any note of the 12 notes and follows a definite pattern. The first note of a scale is called its root note and the pattern it follows gives it a scale type. 

One particular scale of relevance to us is called the Major scale. Starting at any key, the Major scale follows the following pattern:

where W stands for whole tone (jump of two keys) and S stands for semitones (jump of one key).

For example, if you play the notes C1, D1, E1, F1, G1, A1, B1, C2, and back, one-by-one, you have played a C Major scale.  A Major scale sounds uplifting while another scale named minor can sound a bit sad. Don't worry about names—there are hundreds of scales and we just need to know that scales are a sequence of notes played together following a certain set of rules.