Notes in kvCORE can be created via quick actions, or on the contact details page.
Although you can add notes to phone calls, or scheduled calls, they will always be attached to that event. The yellow 'add note' option adds a completely separate note to your contacts timeline.
Additionally, you can add hashtags to notes, and the hashtags you type in will be attached to that contact. This makes it easy for you to organize your contacts as you're dealing with them, instead of having to add hashtags manually.
You may pin any important notes to the top of your contact's timeline for easy reference. Look for the pin icon in the upper right of the note, and click it. You will see the note every time you open your contact, at the top in the 'Pinned Notes' section.