The Matrix field is a rating or Likert scale field, which you can use in surveys and other forms where you want to allow your users to rate multiple items in a single field. To add a Matrix field to your form, click on the Add Field button at the bottom of the Build tab of your form and then click the Matrix button.
Now, you need to come up with Row Choices (shown on the left of the Matrix field) and Column Choices (shown at the top of the Matrix field). You can also set the field to only allow one choice per row or column or to allow multiple choices per row or column, whichever suits your purposes.
This is what the Matrix field will look like on an actual Form:
When you view a matrix field on the Submissions tab of your form, this is what it will look like:
When you export your data to Excel or Open Office, each row in the Matrix will have its own column in your Sheet data, as shown below: