First, you have to make sure the second item in the Book List view does not say Guest Mode Active. Guest Mode Active means you are not logged into the app or if you are logged into the app you haven't synced with the iGigBook server. You sync with the iGigBook server by pressing the icon that looks like two curved arrows at the upper right of the Book List view.
When the second item in the Book List view says "Feature Not Present" with a title of "+$ Drawing Feature", select that item to purchase the feature and wait for the screen to change which signals the process has completed.
To update your version of iGigBook, open the App Store app, search for iGigBook, select the "Update" button. Don't see an "Update" button? You already have the latest version iGigBook!