A sine wave or a sinusoid is a mathematical curve that describes a smooth periodic oscillation. In contrast a square wave is a non-sinusoidal periodic waveform in which the amplitude alternates at a steady frequency between fixed minimum and maximum values. Square waves can be created by adding a large number of sine waves. This process is referred to as "Additive synthesis". The more the sine waves added, the closer the resemblance to a square wave shape. Learn how square wave is formed in detail in this video.
