Having trouble coming up with something to draw? No worries - while you'll eventually learn how to start from a tiny seed of a thought and gradually nurture it into a complex concept to explore through design and illustration, it's perfectly fine not to be there just yet.
For now though, here's an idea that might interest you.
When I was a kid, this group named "Junkyard Symphony" would come to our school and perform for us - they'd grab a bunch of random garbage and out of it, would create the most complex, intriguing musical pieces (at least to my eight year old brain). Today, we'll do the same - though fortunately, ours don't have to work, and nor do they have to be played in front of an audience.
Design an instrument using the kinds of objects you'd find in a junkyard. Everyday things, forgotten things, one man's trash is another man's treasure. You may want to start with an existing instrument and figure out how to swap out its tailor-made components for whatever scrap you can find, or create something entirely new.