The scripts allow's math formulas to be written anywhere within the HTML code. To start a formula you use either a dollar sign $ or you can use a slash and an open parentheses "/(". To end the inline math, you have another dollar sign or a back slash and a closing parentheses. Enclosing in double dollar signs put the math on its own line. Or you can use the backslash and a hard bracket "\[".
If you need to actually use a regular dollar sign in the text, then you need to 'escape' it so the page doesn't think its the start of math. In order to escape it you use a backslash before the dollar sign. "\\$"
Dollar sign before and after:
$y=mx+1$
Parenthesis:
\(y=mx+2\)
Double Dollar Signs:
$$y=mx+3$$
Hard Bracket:
\[y=mx+5\]
In a sentence:
When $a \ne 0$, there are two solutions to \(ax^2 + bx + c = 0\) and they are
$$x = {-b \pm \sqrt{b^2-4ac} \over 2a}.$$