What decentralized applications are and how they work. The principles of the Ethereum platform are considered. Shows how to write smart contracts and use the Geth interactive console to place and transfer transactions. The web3.js library is described, its import, connection to Geth and use in the Node.js environment or on the client side. Demonstrated how to create and manage a wallet service, how to compile smart contracts and deploy them using web3.js and EthereumJS. The Solidity programming language and the Truffle development environment are described. A guide to developing your own blockchain and decentralized enterprise-level applications is provided.