Salesforce Developer Edition is a free, self-service platform that allows developers to build and test applications on the Salesforce platform. It provides access to the full range of Salesforce features and functionality, including the ability to create custom objects, fields, and relationships, as well as to develop and deploy Apex code and Visualforce pages.
To access Salesforce Developer Edition, you will need to create a free account. Once you have created an account, you can log in to the Developer Edition instance and begin developing your applications.