The Pen EEs is a half-frame camera, meaning that for a roll of film, where you would usually get 36 exposures, the half-frame gives you 72 exposures.
It was introduced in 1961 and was the amateur model, with fully automatic exposure and fixed focusing. It is a true point and shoot camera, and has a 28mm f/3.5 lens. The Pen EE family is easily recognized by the selenium meter window around the lens.
The Pen EE.S launched in 1962, is the same model with a 30mm f/2.8 and a focusing ring, made necessary by the wider aperture.
In 1966 the two cameras were slightly modified and became the Pen EE (EL) and Pen EE.S (EL) with a modification of the take-up spool to make film loading easier. EL stands for Easy Loading. You can only recognize them by a small label marked EL stuck on the front, or you can open them and look at the take-up spool.