Responsive Web Design

Hello Designers.

I am a self taught designer. I have a few doubt about responsive design.

  1. As a designer, while I am designing screens to give to to developers, for what sizes I should design screens. I am considering all devices and all possible resolutions…mobile, laptop (windows, mac), tablet etc.
  2. A good resource, link to understand using columns for creating screens.
  3. How to define font for different sizes. I am using material design guide for mobile screens but how for web? For example, If I am using 16px for paragraph in 1366*768 screen then how much should be font for 1440, 1920, 3072 (macbook pro 16"). I am complete confused in telling font size to developer for various screen sizes.

Any other important things that can help me in understanding responsive design.