The dhtmlx spreadsheet doesn't have a UI to generate or administer spreadsheets. Instead you need to need to add a shortcode for a spreadsheet in a post, save the post and view the draft/published page (while loggeed in as an site administrator) to actually edit the spreadsheet.
So in terms of ease of use, it's not for everyone. In terms of advanced spreadsheet features, the developer's web site has generic documentation, but not specifically for the wordpress plugin.
By default the spreadsheet has 50 rows and 26 columns and a ghastly set of text and background colours. I want to change those settings but through the current documentation I can't work out how.
If the developer added an administrator UI which listed saved spreadsheets and allowed spreadsheet settings to be changed then I'd rate it 5 stars. Unfortunately as it is, I can only give it 2.