Another thing you can invest in besides stocks, is to invest in yourself.
For example, my SO is working hard to get a side business going writing romance novels. To do this, she's spent a few thousand of dollars on seminars and conventions with both a learning and a networking component (which has gotten her into a regular work group of published authors), learning as much as she could about the industry, money on cover artists, copy editors, proofreaders, joining promotional anthologies, buying props and make up and books to show off on her promotional social media videos, not to mention all the time in learning this stuff and writing the books.
It's starting to pay off as she already has quite a few followers and preorders for her first book that will release in a couple months, higher than some other established authors in her group. There's some authors she knows personally that were able to make $200k doing this in their first year, so she may be on a similar trajectory at this point.
And she's still working a full time job as a marketing manager (making almost six figures for that) during all this, which she's hoping by this time next year she can quit and do this full-time (needless to say, I've been the main person keeping our house somewhat in order during all this, she hasn't had the spare energy).
So yeah, that's one way you can "use money to make money".