How to make the transition from set dimensions to weights

Hi everyone, new to HN, so please bear with me. In all my formal (collegiate) education thus far, we have been setting specific dimensions for visual elements. I recently got into android development and I really really enjoy it, but it seems like setting specific dimensions in the xml leads to issues with devices that have different sized screens. After a little research, it seems the best way to overcome this, and best practice in general, is to use weights or percentages for dimensions.

My root question is a request for any good resources for learning how to use weights instead of set dimensions. I checked w3schools and didn't find much, but I'm sure I probably just missed something. Alternatively, if anyone knows how to optimize the visual elements of android applications for all device screen sizes, let me know. Thanks!