Final answer:
To complete the key definition after selecting all primary key fields, the 'Save' button should be clicked. This step is vital in various applications, including databases, to ensure changes are preserved and implemented.
Step-by-step explanation:
After all primary key fields have been selected in a database or a similar setting, one must click the Save button to complete the key definition. It's crucial to ensure that every change made to the database schema is properly saved so that the alterations are preserved and implemented within the database. Similarly, this practice also holds for various other computer applications such as document editing or spreadsheet management. For example, when making revisions in a document, one should carefully accept or reject changes using the tools ribbon. Once all edits are reviewed, and comments are deleted, saving the final draft is essential as it ensures that all changes are stored and that the document reflects the latest version.