Posting Questions about LaTeX: Subscripts and Symbols

[annoymage]

Firstly, where do I have to post if i have a question on LaTeX?

and here's the question,

$\vdash_{A}$

how do I make that subscript exactly below the line - on that simbol?

 

[jhae2.718]

\mathop{\vdash}_{A}

will produce $\mathop{\vdash}_{A}$. You could also use \stackrel and play with sizing and spacing.