I have been trying to adjust the CRM template to my needs
From what version of FileMaker? With each version, the design of the starter solutions is a bit different.
Before you work out a layout design, you need to figure out how to add the needed changes to the underlying tables and relationships. If you open Manage | Database | Relationships, you should find a table occurrence "box" named Contacts, or something similar (maybe contact management).
What you will need to do for taking a series of notes about a given contact is to add a related table of notes linked to your contacts table. You can define a new table on the Tables Tab in Manage | Database and define fields for it on the fields tab. I recommend the following fields:
_fkContactID ---> use this as the match field to your table of contacts. Make it the same data type as the field in your contacts table.
While not absolutely necessary, I'd add at least one of the following:
NoteDate----> Date field, set to auto-enter the Note Record's creation date
NoteTimeStamp---> Timestamp field, set to auto-enter the Note Record's creation date and also the time it was created.
You can then link this new table to your contacts table by contact ID's (I'm not giving you the exact name. In most starter solutions that I've seen the needed ID field is named with all caps.) You can enable "allow creation of records via this relationship" to the Notes table in this relationship and then you can add a portal to Notes on any layout in your database where it is based on the contacts table to which you just linked this notes table in a relationship.
This is just the basics. Once you have a portal on your layout for recording notes, you can refine your layout design any number of different ways for recording notes about each contact in your database.