I have read whole tutorial section on sfml-dev.org and have some question.
What are exactly views and how to use them ?
Should I render things in views or in renderwindow ?
Views in SFML, like it says in the docs, are like 2D cameras. Essentially it represents what you would see through a camera and allows you to zoom in or out and to scroll in any direction easily. Doing this with a RenderWindow would mean that in order to zoom in, you would need move/scale every sprite. Same thing for scrolling, you would need to move every sprite on screen depending on the scroll direction.
On the other hand I have used sfml once, to make a multiplayer 2D shooter. I didn't use views at all when doing all the rendering. Everything was drawn directly to the RenderWindow and I had no performance problems or anything else.