cannot display google chart

That’s a chart on Google’s website. This plugin is for taking spreadsheet data and displaying that data on your own site. You can’t embed a /pubchart URL with this plugin.

Look at the screenshots to get a better idea of the procees for using this plugin.

That is because you didn’t follow Step 1 of the example, shown in the screenshot, which is to make your Google Spreadsheet publicly accessible. I promise it’s easier to use when you read and follow the directions.