Followers can broadly be broken down into the following types;
Automata (including T'au Drones)
Bestial Companions
Cyber Familiars
Servitors
To gain Followers, you must make an Influence Test in place of a Wargear Requisition / Endeavour attempt.
In addition, you can gain the service of one of more devotees through the Devotees Talent.
The total number of Followers that a Party can take on a mission is equal to whatever the GM and other players feel is appropriate, to a minimum of zero. In addition, how they can be used is also at GM's discretion, although the following is presented as a guide for balanced play (using the accompanying stat-blocks in the Followers spreadsheet)
Out of Combat: Followers are controlled by their masters through the use of simple commands. These are generally single words, short sentences or the equivalent, and so giving a command is generally a Free Action when not in combat. Certain actions may also require a successful Leadership, Persuasion, or other appropriate Social Skill Test.
In Combat: Followers act immediately after your turn in combat, before the next Threat or Agent, and you must use your Combat Action to make a DN 3 Leadership Test to command them to take any Actions other than Movement. If issued no commands, the follower will act according to it's instincts or programming; at GM's discretion, they may undertake additional Actions depending on the situation.
At the GM's discretion, the follower may have to succeed on an Intellect Test to interpret a contradictory or complex order; alternatively, the DN for the Leadership Test may be increased, or an additional Persuasion Test may also be required.
Beast: Followers with the Beast Trait must succeed at a DN 1 Resolve Test to successfully carry out complex orders from their masters. If within 3 x Rank metres they may add their master's Leadership rating as bonus dice for this Test.
If injured, it must succeed at DN 2 Resolve Test or panic, running 1d6 metres in a random direction (use the scatter template) and suffering from the Fear Condition.
Familiar: Should its master come under attack, a familiar will automatically move to its master’s defence, attacking the assailant unless it receives specific instruction (or possesses an instinct/programming) to the contrary.
Upon completing a task, a familiar will return to its master’s side unless it received prior instructions or some other instinct or programming applies.
Psy-Bonded: A character with the Psyker keyword may gain the following benefits from a Psy-Bonded Familiar;
They can see and hear through the familiar's senses.
They can treat the familiar as a psychic focus so long as it is within a number of meters equal to twice their Psychic Mastery Rating.
They may choose to use any Psychic Power with a range of Self on the familiar instead of on themselves.
They may use their Psychic Powers through the familiar, treating it as the origin point of any power so long as it is within a number of meters equal to the character's Willpower x 5. The psyker is still considered the point of origin for Perils of the Warp.
In addition, every time a Psy-Bonded familiar suffers Wounds, their master suffers 1d3 Shock from the psychic feedback.
Followers with the AUTOMATA, DRONE, or SERVITOR keywords recover all spent Shock after a Regroup, but do not recover Wounds naturally.
Automata, Drones, and Servitors can have Wounds restored via a successful Tech Test, using the same rules as Medicae Tests. Combi-tools, or equivalent supplies, may function in the same way as a Medi-Kit for this Test.