You can connect to your codespaces from your browser, from Visual Studio Code, or by using GitHub CLI. - What are Codespaces?
For now, these docs assume connecting from the browser. When connecting via github.com, GitHub opens a new tab at *.github.dev, where the subdomain is auto-generated by GitHub when you create your codespace. However, the editor is VS Code in-browser, canonically hosted at vscode.dev. See also Hello Visual Studio Code.
All GitHub personal accounts include a quota of free compute time and storage for GitHub Codespaces. Any usage beyond the included amounts is billed to the personal account. - GitHub Codespaces billing
Phew!