Here is a clip of a system I use. It work good for big jobs where you need to cover a lot of ground like foam disinfecting a 30,000 sq ft barn. Foam quality is related to type of soap and pressure. The soap in the video is not a foaming soap, but if you add enough foaming agent you can make shaving cream. And hot water helps foam formation a little.

The foam injectors that go on the end of a gun will operate at a higher pressure and make a better foam. If you are doing a big job the bottle will need to be filled often.

Edit to add that I talk a little funny, but I can't help it.

https://www.youtube.com/watch?v=9YjquX--fME