The aim of this undergraduate thesis was to present the concept of crypto currency and blockchain. To achieve this, it is necessary to become familiar with the history of this technology, basic functionalities and working principles. After introducing the concept of crypto currency and blockchain, the thesis describes the characteristics of the first five crypto currencies according to market capitalization. Each of these cryptocurrencies has different functionalities from which its value derives. In order to be able to use all the functionalities of crypto currencies, you need a place to store them. For this purpose, crypto wallets are used and they are divided into two categories: hardware wallets and wallets built in the form of decentralized applications. In this thesis, the emphasis is on wallets that are made in the form of decentralized applications. To better explain the working principle of such wallets, as a practical part of this thesis, a crypto wallet was developed that functions as a decentralized application on the Goerli test network. All the technology used to develop the application is also described. The background application was implemented in the Solidity programming language, and is responsible for creating a smart contract, setting up a smart contract on the test network and managing user transactions. The client application is built using the React framework. For demonstrating functionalities of application, the Google Chrome internet browser with the MetaMask integrated crypto wallet was used. The application offers the user to send cryptocurrencies to another address and displays the history of all user transactions.