Create a data extension in Salesforce Marketing Cloud
To open the list of data extensions, navigate to Subscribers > Data Extensions.
Click Create. The "Create Data Extension" dialog box will open. You can specify how you will build your data extension.
Standard Data Extension: Creates a brand new data extension with custom fields
Filtered Data Extension: Uses a source data extension and filters data for use in a new data extension
Random Data Extension: Lets you randomly select subscribers from a source data extension
Decide if you want to create from new, duplicate the fields of an existing data extension, or create using a template.
Name the data extension and add a description if desired. Do not enter an external key; Marketing Cloud will generate one upon creation.
Select where you want to save your data extension. Check Sendable if you want to send to this data extension. Ignore the Testable checkbox.
For "Retention Setting", select Off or On as desired:
Off: Data extension data will be kept indefinitely
On: Lets you choose when the data will be deleted and which records. You can even delete the entire data extension.
Under "Fields", add fields to the data extension. Complete the information for each field you need:
Name: The name of the column in spreadsheet/.csv file you are importing
Data Type: The data type of the contents of the field. Values are the following:
Text: Letters, numbers, and spaces (this is the simplest option)
Number: An integer, no decimals
Date: A date value
Boolean: A 0 or 1 value
Email Address: An email address; a field of this type must exist before you can send email to a data extension. You can store multiple email addresses, but when this option is chosen, this is the email address your content will send to.
Phone: A phone number; this data type accepts any string with 10 or 11 digits and strips out non-digit characters
Decimal: A number with a decimal point
Length: Maximum number of characters (including spaces) you can import into this column
Primary Key: The system requires that the value in this field be unique so it can use this field as the unique identifier. In most cases this is the subscriber key (emailaddress.MID# or SalesforceID), which is always unique.
Nullable: As a general rule this should be checked. Determines whether this column can be empty. If you do not select this and you try to import a NULL value for this column, the system will respond as you specify in the "Skip Rows with Bad Data" field on the import definition.
Default Value: If no data exists in the row, it will add this specified value.
Complete the "Send Relationship" field. This determines the field in the data extension that relates to the "Subscriber" table. Typically the subscriber key you imported should relate to the Subscribers on Subscriber Key.
If you marked your data extension to be Sendable (that is, you are planning to send an email to this data extension), then be sure to use consistent, unique subscriber keys so the system will dedupe.