This feature allows you to segment your page subscribers on the basis of custom fields. You can set custom fields values in order to categorise them.
custom fields allow you to save additional information about your subscribers so that you can send more appropriately tailored communications. This means that you can send personalized messages based upon, for example, a recipient’s name or city of residence.
custom fields allow you to create any number of custom fields in each list of subscribers. Custom fields can be in text form (e.g. name, city, phone) or numerical form (e.g. date of birth, date of subscription) or in Boolean form (e.g. Is Active), which is appropriate when creating subscriber segments.
Custom fields will help you to target you campaigns to specific segments of their subscribers list. For example you might have a message that you only want to send to women. Or perhaps you only want to send a campaign to people in a certain age group. Or maybe your message is very specific and you only want to send it to women of a certain age in a certain geographical area.
How to create and set Custom Field value?
2. Select the subscribers you want to set custom field value to
3. Click on Assign Manage custom fields
5. To create a custom field, click on create button. 
5. write the name of the custom field. For example, “Gender” and select type of the custom field. For example, “Text”. Description is optional here. click on create button.
6. Here is your created custom field “Gender” 
7. To change the name of the custom field, click on edit
8.Write the new name for the custom field. For example new name and press the right green icon.
9. To delete a tag, click on delete
10. click on yes. The field is deleted
11. To set custom field value, select the subscribers the same way as in step 2 and click show after creating a custom field.
12. all the created custom field would be shown here
13. To set the custom field “Gender” click Gender Custom Field
14. Enter the value. For example “Male”. and click on save
15. The enter value “male” is now set the gender custom field for one subscriber
16. For Set Custom Field values in bulk, Select the subscribers you want to set custom field values to
16. now click on bulk actions
16. select set custom field option
17. Enter Field Name and Enter Value. and click on save.
You can use these custom fields to send broadcasts, polls, surveys and autoposting