This is the base Jekyll theme. You can find out more info about customizing your Jekyll theme, as well as basic Jekyll usage documentation at jekyllrb.com

Can I use $\LaTeX$ here?

What about a numbered equation:

or even an inline $\Omega$ one?

You can find the source code for Minima at GitHub: jekyll / minima

You can find the source code for Jekyll at GitHub: jekyll / jekyll