Gmail has changed so much in the past two years that referring to it simply as an “email client” doesn't do it justice.
Think of it this way: you could use your smartphone exclusively to make phone calls, or use a MacBook Pro only to create text documents. You could own a sports car you only ever drive a couple of blocks. You could, but there's just so much more these things could do for you, and you'd be wasting your money to only use them for one thing. The same can be said about Gmail, even though it doesn't cost you a dime to use.
This manual is not for new Gmail users, but for those of you who already use Gmail as an email client and want to take advantage of its many features.
Also with this free guide you will receive daily updates on new cool websites and programs in your email for free courtesy of MakeUseOf.