Do I have to make separate applications for phones, tablets and different sizes, or is there a code for this?
You searched it in the community? Probably there a lot of post about this .
Anyway got can work with dimensions in % that could fit good for every device . This is true if the dimensions of the device is similar to your device test.
Or you have to create a code that changes some component according to screen dimensions. Ex if height is more than tot px or if the aspect ratio is bigger than device test etc