Linux is an open-source operating system that was developed in 1991 by a Finnish Software Engineer named Linus Torvalds and FSF (Free Software Foundation).
If you wish to learn Linux and get certified in it, then have a look at the Linux training course from Intellipaat, which offers you 16hrs of training that is instructor-led along with guided projects and exercises to help you gain the required practical skills. Also, have a look at our YouTube video on Linux tutorials made by subject-matter experts.