A conditional contact field is a field on the customer profile with a set of selectable values, where the range of its values is defined by the value of another contact field.
An example of a selectable field is a list of subway stations. In each city, the subway has its own station names; therefore, an online shopper will find it convenient to enter his or her city name and then be able to select a subway station name from the list appropriate to the specified city name and not from all cities' subway stations mixed up in one list.
How to create conditional field "Subway"
For in-cart checkout
Go to Settings app and open its “Contact fields” section.
Click the “Address” field name to open its settings.
Add a new address field, name it “Subway” and select fields type “Conditional (select/input)”.
Click the “Manage conditions” link. Select "Address — City" field as the parent field because the available list of station names depends on the value of the city names specified by a client during checkout. Enter the names of cities on the left and their corresponding subway stations on the right as shown below.
Save “Subway” field’s and all contact fields’ settings.
Go to the Store app and open its “Settings → Checkout” settings. Select the settings of an in-cart checkout storefront.
Expand the “Shipping” block. Enable the newly added “Subway” field and save the checkout settings.
For multi-step checkout
Open backend section "Settings → Checkout", click "Configure" in "Contact information" section.
Add a new field in section "Address fields" and select field type "Conditional (select/input)".
Click the "Manage conditions" link. Select field "Address — City" as the parent field (because the available list of station names depends on the value of the city names specified by a client during checkout). Enter the names of cities on the left and their corresponding subway stations on the right as shown below.
Save the properties of the "Subway" field and the checkout settings in Shop-Script backend.
Done! Now the contents of the subway stations list is updated depending on the city name entered by a customer during checkout.