Depending on the structure of the bay window, curtains or blinds may be added, and there are many other options. A bay window brings more space into a room, and covering it may be done in a multitude of ways.
A bay window that reaches the floor on the inside of a room can be covered with long curtains that complement the rest of the room, as seen on LushHome. However, aside from merely leaving a blank space in the new area offered by the bay window, one can add a small desk to use for studying or working in front of the window. If a desk is placed there, either white or lightly colored blinds can be added so that working is not hindered by long curtains.
Bay windows might have radiators placed in front of them. One can make this arrangement look more attractive with a nice mask that goes over the radiator. Better yet, a bench-style seat can be placed on the entirety of the bay window space. If no radiator is present under the windows, the bench can be the top of a small storage space, which is ideal for keeping track of small miscellaneous items.