HTML is just text, so technically Notepad works. In practice you want an editor that highlights tags, closes them for you, and warns when something's off — VS Code is the common pick, but anything with these features helps.
The fastest feedback loop is an editor beside a browser (or a live-preview pane, like the sandbox on this page). Type, save, see it. The shorter that loop, the faster you learn — and the sooner you catch the typo before it compounds.