First of all you need to add the document to the Google Doc Connector settings. Detailed steps how to do this is described here.

The only one requirement for the doc you add is to have a header with langue codes. Here is the example of the doc structure: Google Doc Localization Example.

The number of languages, tokens, or worksheets is not limited, and can be as big as you need for your game.

Once your localization spreadsheet is added to the Google Doc Connector settings, you may now open localization setting as showed on the screenshot bellow:

Selectet document that you would like to use for the localization with the dropdown menu. Once you done with it, plugin will analyse the document and let you know general info, how much sections is avaliable and how much langauges was found. 

You may use "Expale Settings" button. To see how it should work if you do everything corrently. "Example settings" button will fill Google Doc Connector an Google Doc Localization settings to use this example shpreasheet

When localization document is set, you may now use localization API to manage your game localization. See the Use Guide article.