Servitors are believed to be non-physical entities made by a person.
They take a lot of work, meditation, investment of time and energy.
Some people make them to gather stray energy (whatever that is supposed to mean) and bring it back home for use in ritual practice (as if they can't channel energy from the universe as some believe). Others may create a servitor as protection, to intercept negativity sent the person's way. The options are limited to the creativity of the person deciding to create one.
They can be as simple or as elaborate as the creator believes.
But they are dependent solely upon the creator. They require the person's energy, will, and direction.
Most people who follow this belief will also say that a servitor is meant to be temporary: It is created for a specific task, and destroyed once that task is completed.
Some believe they are between an 'energy sphere' (or some other thought-form of energy with no more than geometric shape of charged energy)and a tulpa (another belief of an independent creature created by a person), while some may say that, if that geometric shape is tasked, it is a servitor. Some will say they have a personality.
But really it all comes down to a matter of belief.