A backend developer is who comes when needs to implement dynamic websites for back-end work. They have to take care of how to connect to the database and servers to the website. A backend developer has to be proficient in languages like Java, Python, Ruby, etc along with HTML and CSS languages. A backend developer also has to know how to handle relational and non-relational databases.
You can enroll this Full stack developer course by Intellipaat if you want to learn both frontend and backend development.
You can watch this video on how to become a Frontend developer if you want to become a frontend developer: