I am playing piano for almost 4 years. But I never played with notes. Now I want to play to notes. I can read them, but I have no idea how I can learn to play to them so fast, that I don't need to look at the sheet so long. What's the best way to learn it?
Try to get hold of some easy piano tutors, even very simple ones for children, perhaps. There are also some very easy pieces by serious composers you might look at. When I started, as a mature learner, one of the things I used at the start was book 1 of Bartok's Mikrokosmos. The first pieces are very simple with both hands playing in parallel one or two octaves apart, and gradually move on to more difficult pieces - and more musically interesting pieces.
You might also do a search for some old piano methods which can be freely downloaded from IMSLP.
Speed, and being able to find the notes without looking at your hands will come with (lots!) of practice. Be patient!
I would also recommend practicing scales and arpeggios as well as learning some theory, as it really helps with the skill of being able to recognize chord shapes quickly, so that you can more quickly take in whole chords and musical phrases with a very quick glance at the sheet music.