The cart and checkout functionalities are added by customizing the shopping cart and checkout
- Steps to customizing the shopping cart
First navigate to Commerce > Websites > Website List.

Click Edit next to a website.
Click the Cart subtab.

Check the box in the Show column next to each column you want to display in your site.
Using the handles on the left side of each column name, click and drag the column to the correct position. The top of the list represents the left-most side of the shopping cart.
In the Width column, enter the percentage of space each column should take, totaling to 100% among shown columns.
Click Save.
- Steps to Customize the checkout
Navigate to Customization > Lists, Records, & Fields > Transaction Body Fields > New.

In the Label field, enter a name for the custom field. This is the name of the field as it will show to customers.

In the ID field, enter an ID for this field with no spaces. This ID is used in attribute tags if you want to call information saved in this field for display in your site.
Select an option in the Type field.
If you selected List/Record in the Type field, select the type of list or record that can be selected in this field.
Make sure the Store Value box is checked to store the information gathered in this field in your account. You should only clear this box if this field is meant for display only.
Check the Show In List box to show information from this field on sales transactions lists.
If you selected List/Record in the Type field, you can check the Record is Parent box to indicate that the record type selected is a parent record. This field is used to create a parent-child relationship between two record types.
On the Applies to subtab, check the Sale and Web Store boxes. Checking these two boxes indicates for your custom field to appear in both your store and on sales orders.
To print this custom field on standard forms, check the Print on Standard Forms box.
On the Display subtab, set display location and enter help for this field
Click the Validation & Defaulting subtab, and then check the Mandatory box to make this a required field. This subtab also includes other options such as Maximum Length, and Default Value.
On the Sourcing & Filtering subtab, decide what options customers should be able to select online. Selections available for sourcing depend on the type of custom field you are creating.
Click Save.