How can I edit my own questions and answers for example, give the symbols for pi, integration, and draw diagrams
You are looking for the Notation page. It provides a mini-tutorial on the use of inline equations and centered equations. For pi, you want \pi and for integrals, you want \int (I'd wrap those with $ to start MathJax, but it is not enabled on Meta).
which can be used to pull an image from a website or from your computer. Also sadly, there is not an easy way to center the image.