Your commentary, which links your three objects to the IA prompt you’ve chosen, should be 950 words long, not including references.
The IB provides a list of 35 IA prompts. Your teacher will probably refer to this list regularly, and carry out formative exhibition tasks to help you get to grips with them, and link them to the course. You should choose one that you can link naturally to one of the optional themes (or the core theme), and one that makes sense to you and engages you personally.
Here are some key points when it comes to deciding on the objects you choose:
Your objects must be different from those of the other students in your class.
You should choose objects that are of personal interest to you - this will help establish the ‘authenticity’ of your exhibition.
Your objects must belong within a specific time & place (rather than be generic).
Objects may be something that you have created yourself (e.g., a piece of work - such as an EE, or a painting for your DP visual art course), but may not be created specially for the exhibition.
Your objects can be physical or digital.
Your teacher will support you during the process of creating the exhibition - and obviously, a key part of this is making sure that you have chosen effective objects.
Clearly identify your three objects and their specific real-world contexts.
Clearly explain the link between your objects and the IA prompt that you’ve chosen, with explicit references made to the prompt.
Offer a strong justification for the inclusion of the object.
Provide appropriate evidence for all of the points you make in your commentary.
Your teacher will give you help in understanding what the assessment objectives of the exhibition are, give you tips in terms of selecting the IA prompt, and advise on the suitability of your three objects. You may submit a draft commentary, which they can give you written or oral feedback on (although they are not permitted to edit this). Obviously, you can ask specific questions as you create your exhibition, which they can answer.
The IB says you should spend around eight hours on creating your exhibition.
There are images and suggestions about what works in a TOK exhibition within the IB website; your teacher should be able to explain how to access these.
You should definitely consult other subject teachers to help you understand the PT you have selected, or the IA prompt (and optional theme) you have chosen. Your TOK teacher should encourage you to reach out to them; they’re a great source of knowledge. Obviously the extent of their help should be helping you to hone ideas you already have, rather than telling you what to write.