Do you have any ideas in mind? Even the slightest vague inkling like "this topic or activity has me curious"? Or are you applying to college because it's the next-thing-to-do and that's what everyone else expects of a high-school senior?
If you don't know what to do, make a basic plan to 1) list out a few things that you're curious about and 2) try them. It's really that simple. Don't get into analysis paralysis. Pick something and try it. If you stick with it and it sucks, try something else. This is real life now, and you're completely free to try whatever you want. The key is to try something though, don't bury your talents in the ground (so to speak) and get stuck in fear. Once you get older, you'll realize anyway that fulfillment is often correlated with your attitude... some activities make it easier to have a good attitude, so it's your mission to find them.
A short aside on College:
When I chose to go to college and bury myself under a crushing mountain of school-loan debt, I went because I had clarity about what I really enjoyed and where I wanted to end up... in my 5th grade yearbook other kids were writing down "singer" and "astronaut", but I wrote down that I wanted to be a "Computer Programmer / Hacker". I had zero self-awareness about it back then, but it authentically came from a heart that loved to build/engineer things.
Don't apply to college with NO PLAN and pray you'll end up somewhere, unless of course you have parents who are paying for all that ;) At the end of the day, this is your life now, and if your plan involves taking a year to figure yourself out, that's a completely valid life course to take, too.