If you are having good knowledge of website development and designing, then it is easy for you to design responsive website.
But in my opinion you should hire website development company for your business website because it is one time activity and one time investment.
You can build a responsive website by following youtube tutorials. Everything is available on the internet. You need to have the basic knowledge of HTML, css, coding. If you are not confident enough, get the help of a professional web developer.
Hello, I am learning web development on behalf of my experience I will give the answer.
To make a responsive website you can use Media Queries, flexbox as a display. Using only HTML and CSS you can customize your site to different levels. Media queries help you most to handle this and it is easier to use and easy to learn. Thank you