i got reply from one of poster
"You can have your default styles for desktops and laptops, then add a media query for smartphones (320px width). And if you think it's best, you can have another media query for tablets with a lower resolution than most desktops.
The key point is designing the page with a flexible layout so that you can adjust to different screen sizes without losing any functionality (or, hopefully, without losing visual appeal). My advice is to experiment with some simple pages to learn the basics of responsive design before you try to make a real website. Once you get some experience with how everything works, it will be much easier to create a page you'll like.
i am going to try , let's see