This optional field on the Versions tab of the dataset is for you to provide further information about this release. You can describe any changes you made or include more details on the state of the data in this version. You can create and save release notes at any point in your process.
When the table is done and you've completed all the fields you'd like to include, you can click the Release version button.
Upon confirmation, the release process will begin. This may take some time for larger datasets — you can leave the page at any time; when the release process is completed, the new version will be available for users with access work with.