They're very different! A roundabout is a road feature - it's a type of circle-shaped traffic junction. Vehicles enter from various directions, drive around a central point and then exit, driving away in another direction. Roundabouts are simply ways of managing road traffic, and they don't involve pedestrians. A square is a feature of town planning - it's where buildings are constructed around a central open area ("meydan" in Persian cultures). Smaller squares often have homes and shops around the edges, while larger ones have civic buildings such as town halls and museums around them. Traditionally, markets have been held in the central part of squares, and these open areas have always been a focal point for people to meet. This is a roundabout: https://thelincolnite.co.uk/2019/03/4-6m-investment-to-improve-a46-roundabouts/ This is a square: https://en.wikipedia.org/wiki/Town_square

A square is an open, typically four-sided, area surrounded by buildings. A roundabout is a traffic circle, often with an island in the middle, around which traffic moves in one direction. You can find an illustration here: https://images.app.goo.gl/q9MQcaPPLbSyKH6G7 I hope this helps.