Most bathrooms don't need an extractor fan but I would recommend fitting one, if anything it helps stop the steam that covers your mirror letting you see your reflection.
I fitted mine quite easy bit I only placed it into the wall, I know you can get some that fit into your window pain I could see them being quite hard to fit so I would stick with a wall mounted fan.
I wanted to have one but I wanted to keep it minimalist and blended with my wall so I decided to fit an embedded one.
I started by making a hole trough my wall, I found it easier by drilling a circular hole and knocking it out wards this stops damage to you interior walls.
You need to clear a space out side before you knock the hole trough and make sure you don't hurt anyone with falling masonry.
Once you have finished this you need to place piping in the hole and cover each end with netting this will stop insects bees etc coming trough the pipe.
Next you need to fit either end of the fan to the wall outside is easy it will screw on, the inside however is more complex you need to fit the electrical wiring If you have minimal experience with electrics I would recommend hiring an electrician.
Once fitted I tiled around the edge this gave it a good Finnish.
You can also fit a pull cord or a switch I fitted a wall switch due to being a skilled fitter but if you can't do this a cord works just a good.