One of the menu options under the Contact Overview menu that is accessible when within a contact record is the Know Your Client section of the contact record:
After clicking Know Your Client, you'll then see the Know Your Client area for the contact and can begin filling in your applicable information for them.
Here, let's look at the Important Info section of this page:
If no data has been entered here, it will be blank as above. To add data, just click the Edit button in the top right corner of this section. You'll then see the below:
The Important Information you enter here shows up in the Important Info widget on a contact's Overview (you can also add or edit this information from that location). It's a good area to track information that doesn't really fit in any of Redtail's predefined fields or that won't work as a Keyword, Personal Interest or User Defined Field. Note that this is a freeform field.
This area might look similar to the below once you've added your desired information:
Custom Exports also allow you to add Important Information as a field, meaning you could create an Export for everyone in your database and quickly see which records have Important Information added (and which ones you might need to add this type of information for).