Note: Even though I open the Creative Cloud site through Adobe Photoshop Touch it can be opened in any browser directly by going to https://creative.adobe.com/
From the main screen to choose whether to open an existing project or start a new one, click the Creative Cloud icon on the top center.
This opens the Creative Cloud website in a browser, click the Sign In button.
Sign in with your existing Adobe ID or create a new one if needed.
Click the upload icon to start the upload process.
Process might differ slightly on a Mac/PC but should essentially be the same.
Back in Adobe Photoshop Touch
Note: Adobe Photoshop Touch supports a maximum 1600x1600 resolution canvas.