The NPC Codex is able to be organized into folders. If you are a GM, click the blue "Manage Folders" button at the top to get started. You can add new folders using the green "New Folder" at the top. By marking a folder secret, the folder and any NPCs inside will be hidden on the Codex from players. However, unless the character itself is marked secret, it may still appear elsewhere on your campaign (via connections or in kinships, etc). Edit a folder by clicking the green "Edit Folder" button in the corresponding table row.
You can sort your folders by drag-and-dropping the handle icon in the left of the table. The order is saved as soon as you move a table row.