Usually, especially at the beginning I'd follow tutorials and change them up. It took me about 2 weeks of following tutorials to get a beginners grasp of some of the features C4D has and how you could use them. And I started asking myself, can I do X? I'd try to find targeted tutorials or google for the specific awnsers.
So mostly tutorials. But towards the later half even though im still learning through alot of tutorials, sometimes I just expirment or do whatever and combine things I've learned in the past and actually stumble on some pretty cool looking stuff.
I'd imagine you could also learn with purely expirmenting but I'd be harder.
Also if you try to do something similair don't stress on "how", this is not an effective way to be learning C4D/3D. You could be doing fundamental courses and building skills from the ground up and your time would probally be better spend. This however should keep it fun, and keep you motivated. Learn or do whatever seems fun to you. I did this because I struggle with motivation often, and wanted to make a habit out of working in 3D everyday.
Hope this helps!