There are two ways to enter mathematical symbols. The first is, to use the panel with mathematical symbols on the right side of the screen. The second is, to type keywords which often is a more efficient way once you get familiar with the names of the commands. The keywords specifically chosen to be intuitive. Also pointing mouse at a symbol in the panel will give you a hint for the specific keyword.
Some of the useful shortcuts:
^ -- raise to a power.
sqrt -- create a root symbol
int -- create an integral sign
pi -- create the greek letter
arcsin, arccos, arctan -- inverse trigonometric functions
po -- create (,) notation for a point
(,) -- create notation for an interval