Not really getting how this bot works or how it's useful... What are its application?

User friendly, the Telegram base users is 60m so potential access to lots of people is pretty huge.
But I think the major use is Coinbase users can access their account through Telegram or a Getgems wallet.
I guess another step toward wider adoption.
Agreed. The 60 million user base of Telegram plus the users of Whatsapp is a huge audience for bitcoin. Even if 10% of those combined users, we will some dramatic surge upward, not only in price but also in adopters and users.

Back to the question, what does the bot do?

Talk to you about Bitcoin.....The perfect woman?
I hope the bot is not that lame like Siri. :v Does the bot answers complicated questions with definite and exact answers? I want to know.

Well it's a bot so it's gonna act like ummm a bot. So Siri like it will be....
I don't use Coinbase but I assume there aren't that many things you need for it to do anyway, send, receive, check balance, etc...it's just a nice layer of user friendliness for newbies.
You know you could in the time you typed asking about it downloaded it and actually tried it....