Commands to edit and modify a formula can be invoked by pressing some key combinations.
Some of these shortcuts only apply when editing math (math mode) some while editing a command, i.e. after pressing the \ key (command mode), and some apply in all modes.
Math Mode Only
Command Mode Only
Some sequence of characters can be automatically translated to symbols. For example, typing p followed by i will result in "π".
If the conversion was not desired, for example you actually meant "pi", type ctrl/⌘ Z to undo it.