To access and manipulate data in a Google Spreadsheet using Ruby, you first need to set up OAuth2 credentials by creating a service account and downloading a JSON file. Then, you can use the `google_drive` gem to authenticate and read from the spreadsheet. Once authenticated, you can insert, update, and delete rows of data using various methods such as `insert_rows`, `update_cell`, and `delete_rows`. The `worksheet` object provides an interface to work with individual worksheets within the spreadsheet. By using a Google Spreadsheet instead of a traditional database for small projects or prototypes, developers can quickly set up and get started with minimal code.