Click on the drop-down chevron icon next to the username found on the top right of the page to access more menu options. Select 'Upload new project'
This is the 'Edit Game' page. Give the game a title, which gets auto assigned as the Project URL. Most of the project's details can always be edited after publishing the project, which includes the title and project URL.
Under 'Kind of project', select 'HTML - You have a ZIP or HTML file that will be played in the browser'.
Next, click on the 'Upload files' button, navigate to the hard disk drive, and select the zip file that was exported from Construct 3.
Once the file is uploaded, the 'Uploads' section will look like this.
Check the 'This file will be played in the browser' option.
'Embed options' gives us a bit more control over how the published project will look. Input the game's width and height values in 'Viewport dimensions'.
Scroll all the way to the end of the page to click 'Save & view page' to see the project. This will navigate away from the 'Edit Game' page to the project's page.