DELETE TABLE is a logged operation, so the deletion of each row gets logged in the transaction log, which makes it slow. TRUNCATE TABLE also deletes all the rows in a table, but it won't log the deletion of each row, instead it logs the deallocation of the data pages of the table, which makes it faster. TRUNCATE TABLE can be rolled back.

A document library is where you upload your core documents. They consist of a row and column view with links to the documents. When the document is updated so is the link on your site. You can also track metadata on your documents.