A "Hello World" of bitcoin?
The easiest way if you come from web development and or you want to put a system in production is to use the most stable and updated implementation/API of Bitcoin Core

note: after downloading it it's best practice to check the md5/sha of the file you downloaded on bitcoin.org to be sure your installer is genuine



1) Install Bitcoin Core 

2) Use it's CLI or JSON rpc APIs: https://en.bitcoin.it/wiki/Original_Bitcoin_client/API_calls_list

there's no step 3!



This in the case your target is to run an app connected to most of the updated nodes, have the latest code with security fixes to at least sign and broadcast transactions, and obviously, query the blockchain!

glhf