I've been taking this course for about two weeks now and I've learned a lot more about using the command line than I had in 2 years of beginner distro hopping and experimenting. I find myself doing more and more in the command line because it's faster and more intuitive once you know what you're doing.
The course is free and provided by the Linux Foundation. You have lifetime access to the course materials once you've signed up. Should you want to receive a certificate, you can do so for $99 once you've completed the course.
Hope y'all find this helpful.