How to type Sigma and other symbols in MathJax [duplicate]

Can someone please illustrate how to use the sigma symbol using mathjax and other such symbols please help? By the way the moderators of this site are extremely helpful so thank you.

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• Type \Sigma inside dollar signs: $\Sigma$. Search for mathjax tutorials and detexify. – littleO Jan 8 at 15:28
• Type \$\Sigma\$ – John Doe Jan 8 at 15:30
• – Martin Sleziak Jan 8 at 16:00

\$\Sigma\$ produces

$$\Sigma$$

\$\Sigma_{n=1}^\infty\$ produces

$$\Sigma_{n=1}^\infty$$

\$\sum_{n=1}^\infty\$ produces

$$\sum_{n=1}^\infty$$

and \$\displaystyle \sum_{n=1}^\infty\$ produces

$$\displaystyle \sum_{n=1}^\infty$$