"Profit" is simply "bringing in more money than you spent to create/achieve X task."
If you bake cookies, and the ingredients and stove fuel work out to cost you 15 cents a cookie and you sell them for 25 cents a cookie, you've made 10 cents profit.
The real question is whether you can live on those profits.
Over the entire batch of cookies, how much does the 10-cents-a-cookie add up to? How long did it take you to bake the cookies? What is your time worth? What did you not do while making those cookies?
It's the same with anything else. Yes, you can write a novel. How long will it take you? What did you not do while writing that novel? How much will it cost to publish? After you sell a copy and subtract the publication costs, what's left?
Even writers with contracts from publishing companies may struggle to live on the profits (the royalties) if the book isn't a gangbuster (and really, how many are). So you may "make a profit," but you have to figure out if that profit will pay your bills while you spend all your time writing the next one.