You can make changes to the table structure and properties in Design view.
You might find that a database you've received isn't comprehensive enough. Perhaps you need to add another field to hold more data.
If you want a new field to show up in your forms, you'll first need to add it to the table that the form is based on.
The table opens in Datasheet view. Although you can add a new field there, it's usually best to switch to Design view, where you can specify other settings.
After you add the field, you can set its data type, such as whether the field contains text, numbers, or a yes/no answer.