I'm new to shaders and know that you can color pixels with gl_FragColor but sometimes there is this thing:
vec2 uv = gl_FragCoord.xy / screenSize; // or resolution or smthn depends on the implementation
If gl_FragCoord is like pixel coordinates, what does uv get?
Why is it often done in GLSL?
If someone could even draw an example of which part of the screen will be UV it will be very helpful!