How to create Data Extention in Salesforce Marketing Cloud?

Create a Data Extension
Follow these steps to create a data extension in Marketing Cloud Contact Builder.

Click Data Extensions.
Click Create.
Select the data extension method in the Creation Method dropdown menu:
Create from New - create a data extension and manually insert all attributes
Create from Existing - create a data extension and include all attributes assigned via the existing data extension, or add attributes later in the creation process
Create from Template - create a data extension and include all attributes assigned in the template, or you can add attributes later in the creation process
Enter a name for the data extension in the Name field.
Note the external key provided in the External Key field. Use the provided external key or enter a unique key of your own in this field. Each data extension must use a unique external key.
Enter a brief description of the data extension in the Description field.
Click Change Location and choose the location for storing the data extension:
To use an existing folder, click the folder and click OK.
To create a folder, click Create New Folder and name your folder. Select that folder when you complete the creation process.
Select the Is Sendable? checkbox to make this data extension available as the source of a send.
Select the Is Testable? checkbox to make this data extension available for testing.
Click Next.
To set a data retention policy for your data extension, click On under Data Retention.
To apply the data retention policy, click the button under the Apply To heading for the entity or entities.
Click the appropriate button under the Retention Period heading:
For a revolving time period, enter the number in the text field. Select the unit of measure in the dropdown menu next to the first button. For example, you could enter the number 6 and select Months in the dropdown menu to enforce a 6-month data retention policy.
For a set date, select the date next to the second button.
Click Next.
To make the attribute include the unique identifier for all records within the data extension, choose the Primary Key checkbox.
Enter a name for the attribute in the Name field.
Choose a data type from the Data Type dropdown menu.
For decimal data types, enter the maximum amount of numbers in the first text field. Enter the amount of numbers to appear to the right of the decimal point in the second text field.
Base16Encrypted
Base16EncryptedEmail
Boolean
Byte
Date
Decimal
EmailAddress
Locale
LongNumber
Number
Phone
ShortNumber
Text
If the attribute must contain a value for every contact, choose Required.
To allow in this attribute in the Length field, enter the number of characters.
To force the attribute to contain a value by default, enter that value in the Default Value text field.
Note
Repeat steps 12 through 17 for more attributes within the data extension.
Click Create.
Click OK.