As a beginner and someone who is happy to learn at a fairly slow pace I'm not necessarily in a rush to do anything real serious, but how much grasp should I have on a language before I start bashing my head at making a thing?
It depends really on how you best learn things. But there's an awful lot about programming that you *only* learn from making your own things, and one of the key skills of programming is knowing how to look up stuff that you don't understand - which is something you have to do a whole lot of first time you make something!
It's as well, though, in order to avoid taking yourself down blind alleys, to have a reasonable grasp of what sort of thing the language can do, even if you don't understand the details.
There's no earthly point in delaying making something until you know everything about the language, because nobody ever does. Every language has quirks, opportunities, idioms and idiosyncrasies that don't make it into courses and books and have to learned on the job.
What I usually do is speed-read a textbook two or three times first. Not so I understand everything in it, but so that when I reach a sticking point I have some grasp of where I need to be looking for an answer. Then I dive into making something straight away, just because that's the way I learn best.
You might find you work differently. If you're happy working through whatever it is you are working through and it doesn't feel like a chore then that's fine. But the first time it starts to irk you and you want to get started on something, then go for it, because it is a hell of an incentive to learn more everytime you get stuck on something.