They are vinyl window stickers. Removable, but not reusable. They are rated to last 3-5 years outside, but car washes with high pressure can take them off sooner. The small ones are about 5.5x3.5 and the larger ones are about 7x4.5.
The "reverse image" ones you would apply inside of a regular window to help them last longer (not exposed to the elements/car wash). They will also come with transfer tape attached, so you can easily apply them, as well as basic instructions.
If you have tinted windows, you will want the regular image and apply on the outside. If you have clear windows, the reverse image ones can be applied on the inside to help protect them and make them last longer.
Here is the video to install: https://www.youtube.com/watch?v=PveRwpmsQKo