In order to open and edit your document from any of Xara's desktop products that's - Designer Pro+, Designer ProX, Web Designer, and Photo & Graphic Designer - you will need to...
Save your file locally either as a .xar or a .web file (File > Save as... )
Upload it to one of your chosen cloud storage providers (Google Drive, Dropbox, One Drive).
Open Xara Cloud in your Browser.
Select the cloud provider to which you uploaded the file to from the top.
Navigate to the folder where you uploaded your file.
Using cloud storage ensures that you and your shares are always working from the most current Xara file. The newer versions of the desktop products ensure a "seamless" integration.
If you want to publish your documents to the web you will need a separate account. If you own a desktop product then free web hosting is available for a year.
See here for details...
Also see this article for info on publishing to the web using a desktop product and Xara Cloud...