How can I frost indoor windows?

I used frosted contact paper on the inside of my storm door leading to my sun porch. I did this 2 years ago and still looks great.It was also the cheapest way to go.

Here are a few different ways:

https://www.wikihow.com/Frost-Windows

You can buy window privacy screen from Amazon and other retailers. Almost all of adheres without adhesive so it can be applied and removed without having any mess to clean off the window.

They also make spray on frosting by Krylone for glass. I really like the non-adhesive window film, and it comes in a lot of designs and solids. Amazon has the best collection.