When you Archive an Article, the content is put into a state which removes it from your site as published content. The Article is still available from within the Control Panel and can be retrieved for editing or republishing purposes. Trashed Articles are just one step from being permanently deleted but are still available until you Remove them from the Trash Manager. You should use Archive if you consider an Article important, but not current. Trash should be used when you want to delete the content entirely from your site and from future search results.

To completely remove an Article, select the Articles that you want to delete and move them to the Trash. Next, open the Article Trash in the Content Menu and select the Articles you want to delete. After deleting an Article, it is no longer available as it has been deleted from the database and it is not possible to undo this operation.

Well you are reading it right now! This depends on what you want to achieve. If you are new to Joomla! and have no clue how it all fits together, just install the sample data. If you don't like the English sample data because you - for instance - speak Chinese, then leave it out.