I read the answers and I'm not getting it. Some of them tell me to use preferences, others tell me to input
%!TEX option = --shell-escape
at the start.
Here's what my screen looks like, to show you that Idk where the Preferences tab is.

Basically want to convert that pic to png.
For efficiency in providing solutions, I'll provide the code in case there may be anything wrong with it:
\documentclass[convert=true]{standalone}
\usepackage{amsmath, amssymb}
\begin{document}
\(\{P,Q\}\vdash R \)
\end{document}
It would be a great help to fix this. Thanks.
EDIT. Here's the result after adding the --enable-18 as requested.


shell-escapeor do you just not haveimagemagickorghostscript? You need one of those to do the conversion (see manual ofstandalone). – TeXnician May 06 '17 at 12:58shell-escape. Please read the manual! – TeXnician May 06 '17 at 13:00