In that context profit is what's left once revenue is received and expenses paid.
Implicit in those expenses are (fixed) salaries, employee contracts, payslips and so on.
What a business does with the profit can be varied. Firstly it can be added to cash reserves, which can contine to pay expenses through poor-revenue months. It might be spent on assets, like new hardware. It might allow for another hire. In some cases, although less often than you might think, it pays out dividends to owners.
You don't mention too many details, so I can only presume your situation. I suspect it's a different kind of setup. If you are man-alone, and the project is small, (ie you have no desire or need to add a employee) then basically the revenue is just income to you. Some months you get more, some months you get less. In this context there isn't "profit" but revenue. This is especially possible for software where other overheads are trivial and the effort of tracking expenses for tax purposes meaningless. You may not even keep a set of books.
If you are indeed in this space, then I understand why the article feels unrelateable. It's discussing a very different situation.
As with all articles of this nature, context is important.