The page you are reading is part of a draft (v2.0) of the "No bullshit guide to math and physics."
The text has since gone through many edits and is now available in print and electronic format. The current edition of the book is v4.0, which is a substantial improvement in terms of content and language (I hired a professional editor) from the draft version.
I'm leaving the old wiki content up for the time being, but I highly engourage you to check out the finished book. You can check out an extended preview here (PDF, 106 pages, 5MB).
Calculus is useful math. Useful for physics, chemistry, biology, business and all kinds of other areas. You need calculus in order to do quantitative analysis of how variables change over time (derivatives) or sum up all kinds of contributions that add up to a total (integration).
We will begin our study of the subject by a review of basic math, which we will be necessary throughout our study of this material. Then we will look into the concept of a limit $\lim$, which is pretty much the only new mathematical concept that will be required.
Starting with limits, we can define the concept of derivatives ($f'(x)=\frac{df}{dx}=\lim_{\Delta x \to 0} \frac{\Delta f}{\Delta x}$) and integrals ($\int_a^b f(x) dx$).