There are two modes for equations on the LibreTexts (and mathjax / latex in general): inline and display. 

Inline equations are designated with \( and \) delimiters and are a meant for being embedded in text. As such, they do not have equations numbers associated with them.
Display equation are designated with \[ and \] delimiters and are means to take up a full line by themselves (i.e., no text before or after). BY default, the LibreTexts adds an equation number based off of the the number in the title of the page (if no number, then just starting from one). This can be removed by adding the \nonumber or \notag code in the equation.