The gray block is the object. You can enter values into the text field to change the density of the fluid or the object. There is a drag force Fr when the object is moving in the fluid. V where V is the object's velocity. Click the LEFT mouse button in gray block and drag the object to some other place.
Numbers shown in the upper left pairs are the X coordinate and the width of the object.
Number shown in the upper right pairs are the Y coordinate and the height of the object. The mass of the object is shown in the textfield. You can drag the object and let it submerged in the fluid. Black vector represents the weight of the object. Black circle is the center of gravity .