It's a combination of course, like anything in life. Partly you gotta know what the heck you're doing, how the tools work and such, what the rules are, if any, but partly you just dive in and mess around. Music, painting, photography, parenting, writing, comedy, love... You name it.
My learning has been a combination of trying things out, seeing what doesn't work, trying something else, getting frustrated. Then I found these forums and realized that it's actually pretty easy to use. Don't let the dozens of controls scare you. Just learn one thing at a time and move on to the next thing.
Good luck!
PS. My first few renders were pretty bunk. 18 hours just to see some lumps on a hill with a tree somewhere. But I was fascinated, so I kept at it. (The first pic is my first render. The second one is what I did after doing the "wilderness" tutorial.
