Account owners can set up custom fields to track additional data.
There are four types of custom fields:
To set up or view your custom fields, log in as the account owner and go to Admin > Custom Fields.
Please note that for sorting to work correctly, the custom field needs to have the correct field type. For example, a Birthday field needs to be set up with Date type; whereas, fields like Commission or Number of Page Views need to be a number.
Custom Fields Location
Custom fields appear on the left side of the contact record:
You can display custom fields on the People screen by clicking the "Columns" button and ticking custom fields to display:
Sorting & Filtering by Custom Field
You can also filter and sort by custom fields on the People screen:
More Info Here: Filters & Smart Lists
Merge Fields in Email & Text Templates
You can use any of your custom fields as merge fields in email and text templates.