The Microsoft Access interface is a great deal more complex than say that of Microsoft Word or Excel and at times can seem downright impossible to master. Here is the most common scenario I see where a user becomes “trapped” in a situation — and how to escape it!
Essentially what happens is that you are in a table in Datasheet view and you put your cursor in the New Record row and then try to switch to Design View or close the table. The problem is that you have begun the process of adding a new record and that “new record” as such does not fulfil the requirements set for the fields in that table.
You must either reverse what you have done and “convince” Access that you are not adding a new record, or you must simply add values that fulfil the requirements of the fields for that table so that the new record can be saved. You can always delete that “escape” record once it has served its purpose.
This situation is reproducible and is worth practising so that you are not flustered should you encounter the problem during an assessment where it can be incredibly disruptive.