There are several common ways to emphasize a word in text in an email or chat message. The least desirable way is with capitals, which indicates shouting, and is considered as rude as real shouting.
This is VERY HARD to understand.
A good method of emphasizing words is to use stars.
This is the *funniest* movie he’s made yet.
You can also use underscores to indicate underlining:
That is _exactly_ what I thought!
Quotations are the standard punctuation for titles:
My favorite book is “Lord of Light”.