Simply type ALT and = at the same time, and you will enter equation mode. You can then write in symbols. It's mostly similar to latex, with slight differences. In fact, it's better and faster than latex most of the time.
If you have a version less modern than 2007, then click insert, then go to object. It should produce a list. On that list there should be something called "equation editor 3.0" or "microsoft equation 3.0". Something like that. If you enter this mode, it allows you to insert mathematical equations.