When you create a plug-in using a template wizard, the manifest editor will contain one additional page - the Welcome page. Its purpose is to summarize the content that was generated by the selected template, and help you be productive quickly.
Once you get more familiar with plug-in development and modify the plug-in significantly, you can stop the page from appearing by selecting the checkbox at the bottom left corner. Once you close the editor, the page information will be removed and will not appear the next time the manifest is opened for editing.