As internet revolutionized information sharing, blockchain will do the same on how values are transferred (money, stocks, bonds, properties).
Blockchain (the internet of value) is disrupting intermediaries because a trusted entity is not anymore needed to transact value. Ethereum blockchain is the trustless network for transacting. All industries (financial, legal, tech, supplychain, art & media) are moving towards it to reduce their costs.
Smart contracts are programs running on the ethereum network. When deployed, they are autonomous, and could serve clients (against negligible fees ~0.15$) without human interaction, trusted company or hardware hosting costs.
Imaging a smart contract "uber": where there is no back-office employee, no fee for hosting their infra, or managing transaction. A client orders a taxi through a mobile app (built by a crowdfund open source community), pays $10 for the car ride through the smart contract, and the driver gets all his added value $10-$0.15 if he complies to all the rules of the contract (client has validated that he reached his destination). Same network fees (~$0.15) apply if he had used a private jet, or sent $1 Million to a friend, no entities in the middle (uber, banks, visa) take their cuts.
This docker compose deployment will give you, in one command line, all the tools you need to build up a full environment to access ethereum:
Follow the github to get step by step instructions to deploy your ethereum infra running on docker: https://github.com/gregbkr/geth-truffle-docker
From here you can start test/deploy a simple HelloWorld smart contract and learn more about the ecosystem and commands.