In order to learn C programming language, it is advisable to first learn the different terms, syntax, and commands that are available to use. You can accomplish this by purchasing a book, enrolling in a programming school or you can simply search online for sites that teach people how to program with the C language.
In terms of relevance, all programming languages are relevant and unique to each scenario. You can learn the C language as a backbone language to introduce yourself to the world of programming, or you can simply use it to create programs that you need for your business, studies and personal life.