Is it necessary to bind objects (say cards) to the row grid when designing an android application?

Question

Android

I am designing an app for the first time. What should be the binding of screen objects? Should objects be scaled in height? Why is mdpi different in some articles ( 320x480 dp, 360x640 dp) And, accordingly, under which screen to design, if the application is designed for use with a minimum of Android 4.4