How to develop a responsive website design?

Question

Design

It is necessary to develop an adaptive design for the site from scratch (in Photoshop). So that there is one content, but it looks correct both from the web and from the mobile application. Where to start with regards to technical parameters? (Dimensions, grid, etc.)
Thank you.

Answer 1

1) Read an article about the design of adaptive grids
2) Read a more technical article about the layout of adaptive grids (to understand the layout designer's problems)
4) Decide on the number of "breakpoints" (for example, three - desktop, tablet, phone)
3) Start by building a grid (three breakpoints = three layouts)
UPD: look at examples of responsive designs to understand how they behave (how they should behave)

Answer 2

viewportsizes.com
screensiz.es/phone

Answer 3

And what - "grid"???
It is also in Africa 12-column or 16-column.

Answer 4

You need a separate design for the PC and separately for the phone. As a rule, a design from a PC is pulled onto the phone, with some changes.
On a PC, I make 12 columns - 1070 pixels, for a phone - from 380 pixels. (4 columns)