When the narrator needs an NPC, they will often need one of the mortal species (that is, a normal character that the players can interact with). If a creature of beast is needed, the Bestiary is the go-to source, but for "regular" NPCs, there are several options.
First, if the occupation of the NPC is the most important part (that is, is the NPC a guard, a tavern keeper, or a queen), then the mortal entries in the Bestiary (such as Bandit) are a great and easy choice. The attributes and talents are designed to emphasize a typical character in that profession. The narrator is encouraged to embellish the NPC by providing details such as species, but can simply use the entry in the bestiary for all mechanical components. This is a great choice for entirely disposable or ad-hoc NPCs; characters that likely don't have a name or backstory.
Second, if it is important to do so, the narrator can use the bestiary entry, but simply replace the attributes with the ones that correspond to the mortal species found in Species. The narrator can go a step farther and also include that species' perks (where relevant). This is a great choice for a less disposable NPC, such as a bartender the players will return to throughout the story.
Finally, for important or major NPCs, the narrator can simply make a full PC using the rules provided; the character will still be an NPC, so certain restrictions apply (such as no critical successes). This NPC can start with any amount of story points the narrator deems appropriate to balance their encounters.