Are there any planets/ stars which are not in a circular shape, like squares shape planets. Read.?

No, in fact the definition of a planet (or one of the best definitions, at least) is a body which is big enough for its gravity to pull it into a roughly spherical shape. Anything bigger than a large asteroid can't really overcome the force of gravity, hence why all larger objects are roughly spherical. The only deviations are those caused by rotation and/or gravitational interactions with other objects, which cause some objects to become slightly bulged. Our Earth is a good example - it's actually called an 'oblate spheroid' because its rotation causes it to bulge slightly in the center.