How to earn my first bitcoin in baby steps? I don't know any thing about bit coin , what I know that it digital currency maintained by people and not banks.

How do I start earning my bitcoins ? OK After earning this bitcoins ? What all things I can buy in real world or it just to pay for only services to service provider?
HOW TO BUY BITCOINS

1) From exchanges. Exchanges are many based on countries. UNOCOIN is a popular one for India. Alternatively, if your nationality is different from what I presumed, you can have a look at this site for many exchanges and wallets: COINDESK. You can create a bitcoin wallet here: BLOCKCHAIN

2) Have a look at this link for more detailed explanation: How do you obtain bitcoins?

WHERE CAN I SPEND THEM

You can spend them on websites/services which ACCEPT bitcoins as a mode of payment just like Paypal, Credit Card or Debit Card.