How can I type math symbols in this forum, like set operators, etc.?
If this question is repeated, I am sorry I just searched and couldn't find an answer.
And could anyone give me hint to use Tags for this question?
First, once you get $5$ reputation, you can ask this on http://meta.stackexchange.com Never mind that, it will only get closed as a duplicate of the MathJax tutorial I will talk about below.
Hope I helped