My friend circle told me that more money income by wordpress,is it true? And how will I learn about wordpress ?

No, that isn’t true. The barrier-to-entry is low, therefore the competition is extremely high.

To learn WordPress, you’d want to visit the WordPress codex that you can find over at wordpress.org.

There are so many good resources on the internet that a search in your favorite search engine will give you an abundance of results. My favorite site probably is perishablepress.com. WPBeginner is also a solid resource.

And there are many books. If you do a search here in the forums, you’ll be

too much competition.
you can try to earn different ways:
custom these design and development
custom plugin developer

then again earnings would depend on how good you are, plus it takes lot of time to establish a reputation.