Question about App Pictures

Hello. I don’t know where can I get images for my app, where?
And also can it be like some picture on a peace of paper and then placed in the app like a View?

There are a number of web sites that have images you can use in your project but in many cases you need to give credit to the author if you use the images in an App that you place in the App Store.

Have a look at unsplash.com

How much is one picture cost approximately?

The images on https://unsplash.com are free. All you have to do is attribute the author if you use the image in an App that is on the App Store otherwise personal use requires no attribution.

See this licensing page on the unsplash web site: https://unsplash.com/license