First make sure that you have created an account on itch.io
Click on your username and then Upload New Project
Fill in the details.
Note if you have an HTML5 export make sure that you have an index.html file and zip the folder up. This will mean that you can play the game in the browser.
Most uploads will be left set as Downloadable
Upload your game files. It’s a good idea to compress the files into one zip folder to make it easier for people to download.
Fill in the details and upload images of your work to the page.
Modify the settings for Community and Visibility and Access to suit your needs.
If you are in development and want to allow certain users access to your project page select Restricted.
When you are on your game project page you can click the Secret URL link to get a URL that you can give to people so that they can have access to your work even when the project is set to Draft.
Congratulations you have now creates an itch.io project page.