This deliverable is a domain model of your system with a superimposed world diagram.
Decide on the entities in the world of your system and capture them in a domain model expressed as a collection of rectangles, one for each entity, as shown on Slides 47 and 49 of the slides about the Requirements Engineering Reference Model. (Hint: the nouns from a one-page summmary or vision document from your client or from your team's project abstract would be a good starting point for the entities that should be in the model. This summary, vision document, or abstract is generally written at the user level.)
For this deliverable, it is sufficient to show only the name of any entity as in the diagrams in the Requirements Engineering Reference Model slides. It is not necessary to show attributes and operations as on Slide 21 in the Classes & Concepts slides. You will be dealing with the operations for the Use Case Model deliverable. If you want to show this information for your purposes, your TA will only comment on it.
In order to help you not to go into implementation details, your model should have only one item in the system that is not in the interface that is called "X system", where "X" is the name of your system. This item is effectively the black box that hides all implementation details.
Then divide these entities into the environment and the system. Superimpose this division on the domain model diagram. You can do this superimposition by drawing a shape enclosing the environment entities and another shape enclosing the system entities; then label each shape as ENV or SYS as the case may be, as shown on Slide 48 of the slides about Requirements Engineering Reference Model or on Slide 37 of the slides about Classes & Concepts. Alternatively, you could create labeled regions that include the relevant domain model entities as shown on Page 21 of the slides about Classes & Concepts. Still alternatively, you could just mark each domain model entity with "ENV", "SYS", or both, as the case may be.
If you have done this superimposition correctly, you should be able to see clearly which entities are in the interface.
The basic model should not be more than a page or two, and if it is, you're probably describing too many implementation details.
You may include in this deliverable a list of any question that you have for your customer about your system. These should be clearly marked as questions.