What Is A Tulpa
A tulpa is a consciousness parallel to your own that is self-aware, can think, has free will, has memory and (can have) appearance they self-identity with. They are independent of their creator's consciousness, but share the same body and sometimes some parts of the mind.
A tulpa's personality is a product of the unconscious mind, your consciously chosen traits, and the emergent consciousness of the tulpa itself. It is developed through interactions and conversations with the tulpa and through personality work, which can have many forms. A tulpa is not a personification of your subconscious, they are their own consciousness.
A tulpa can think on their own, has their own decision-making skills, their own preferences, opinions and tastes, and all of these can be distinct from your own (no matter how similar or dissimilar they may be). They are able to talk and function on their own. They exist within the mind, and thus can easily interact directly with other consciousnesses in the same mind, such as their creator and any other tulpa occupying the same body. There are a number of ways a tulpa can interact with someone or something outside the body. For example, a host can relay what their tulpa says, or can allow the tulpa to control the body directly.
A tulpa's form is an imagined body existing in mental space, which they associate with as an extension of themselves. This form can be chosen during the creation of the tulpa, or can emerge naturally from their personality or the subconscious. A tulpa often self-identifies with their form, but may change it if they desire. These changes may or may not be more drastic than simple alterations, and may include total transformations of appearance. The form can act as a reference point for interacting with a tulpa, and allows for methods of visual communication and expression, such as body language. The form is initially seen in the mind's eye or in daydreams, but can be made externally visible to the host as a controlled hallucination.
In conclusion, a tulpa is first and foremost a consious mind that often identifies with a form, created by an individual as a mental companion. There are many reasons for doing this, some of which are mentioned in the FAQ.
If you have any further questions about what a tulpa is like, how to create one, or anything else, please consult the other guides available here, FAQ (Frequently Asked Questions) or ask a question on the forums if the question isn't answered somewhere else.