Hi Jimmy506, Welcome to EasyEDA. Square pads are generally used to indicate pin 1. Other than that they have no generally accepted significance. In other words a 3 pin single row header would have a square pad indicating pin 1 at one end, a round pad assigned to pin 2 in the middle pin location and another round pad assigned to pin 2 at the other end pin location. Pin polarities are not usually marked in the pad shape but may be via the silk screen. Most connectors are polarised in some way so polarity marking is not often needed whereas pin 1 indication is useful when probing a PCB with a DVM or scope. I have sometimes used a square pad to indicate pins 1, 11, 21 etc on multipin connectors. In EasyEDA you can assign other pad shapes if you wish. Ovals and rectangular pads are easy to create.

@andyfierman Thanks very much for the thorough answer. It is very much appreciated!