Creating a Customer Segment 

1. After logging into Magento go to  Customers > Customer Segments
2. Select "Add Segment" 
3. Here we have basic information,

• Segment Name (required field) – This is for internal purposes.
• Description – This is also for internal purposes, and provides an optional space to enter more detailed information than can be contained in the Segment Name.
• Status (Active/Inactive) – Select Active to enable this Segment.

4. Select "Save and Continue Edit"
5. Under "Condition", you have to create a simple rule. 
       Ex. Target customers with a specific email to give them a discount

6. Checking Matched Customers