You can claim to know just about anyone - and maybe you really do! Your life history should include at least some details about your relationships - good, neutral, or bad - with other people in the game world.
It costs points to have associates you can rely on for assistance during an advanture. Likewise, individuals who complicate your life or actively seek to thwart you, personally, are worth points as disadvantages. Note that these NPCs need not be people - they might be spirits, animal sidekicks, or robots.
Some friends and foes physically enter play when they appear. These 'associated NPCs' have personalities, life histories, and character sheets, just like PCs. In each case, the GM will interview you regarding the attitude, character story, and general abilities of the NPC, and then use this information to create a character sheet.
Character sheets for Associated NPCs - like those of all NPCs - are for the GM's eyes only. You will not have access to them! When these NPCs become involved in the game, the GM plays their roles and control their actions. Thus, even your closest associates are never 100% predictable.
Buy advantageous Associated NPCs as Allies or Patrons. Disadvantageous ones include Dependents and Enemies. The GM's word is final in all cases. The GM is free to forbid an Associated NPC that he feels would be disruptive, unbalanced, or inappropriate. He might even choose to forbid entire classes of NPCs - Dependents, Enemies, Patrons, etc. - if he feels they would unduly disrupt the flow of the game.
You may also have associates who provide useful information or very minor favors, but who do not become physically involved in dangerous adventures. They appear only for long enough to help out, and then quickly depart. The GM will roleplay them and give them personalities, but since they are no more likely than any other friendly NPC to get involved in the action, they do not require full character sheets. Purchase such NPCs as Contacts or Contact Groups.