Visual Studio(VS) Code has built-in support for viewing HTML pages within the editor itself. You can follow below steps to open a browser like window in VS Code:
Open the command pallete (Ctrl + Shift + P)
Type Simple in the command pallete and then select Simple Browser: Show from the list of suggestions (Refer screenshot):

Enter URL in the URL box:

Press Enter
Also, there is a shortcut if you need to open the current page in a real browser e.g. Chrome, Edge, etc. You will see an arrow button in top right corner of the browser (Refer screenshot). When clicked, it'll open the current HTML page in the default browser of your PC.

Note: There is a difference in the behavior of VS Code's built-in browser and real browsers like Chrome or Edge. You cannot load any HTML file directly from disk unless you host it in a web server e.g. Live Server extension in VS Code, NPM Server, Apache, IIS, etc. So you can't open an HTML file in VS Code browser tab by providing a local computer drive path like C:\temp\mytestpage.html. It has to be a web URL e.g. https://localhost/mytestpage.html.
Credits: John Henry's answer