Where do those people get all the data from ??..

Hi guys,

 I have been looking for a place where i can fetch the bitcoin and other crypto currency market data.
 Where can i get the market data of bitcoin and other crypto currencies ?.  If there are no official api's is there any documentations i can look about getting data from the block chain ?. 

  I visit coinmarketcap  for checking bitcoin market data. I am just wondering where coinmarketcap get all the crypto currency data from ?. anybody have any idea ?


regards,
Jijo John

Greetings guys,

   I am new to the bitcoin ecosystem. I used some websites like coinbase and stuff..

I am just wondering... 
 
how did exchanges find  initial buyers and sellers ?.
How did poloniex , coinbase and others got all the users ?.

your help would be appreciated.


Thanks,
Jijo John

Greetings guys,
    This is JJ. I have a question for you guys.. I am a programmer and want to create my own wallet for android. How can i create one ?. Any sdk's or any libs available ?.

Thanks...