You ask about broadsheets and tabloids. Broadsheet newspapers are the "big" ones like The Australian, The Sydney Morning Herald and The Age. Tabloid newspapers are "small" ones like the Melbourne Sun, The Daily Telegraph, the Adelaide Advertiser and (now) the Brisbane Courier-Mail . . . it doesn't like the term "tabloid", and calls itself "compact". Tabloids are usually (not always) more sensational, and the broadsheets are usually (not always) more serious. That's why the expression "tabloid journalism" is usually a derogatory term meaning cheap sensational journalism. The much revered London Times has changed from a broadsheet to tabloid size.
The words began simply as a description of paper size. A broadsheet was the big, wide sheet you had to spread across the breakfast table and fold in half to read. A tabloid was half that size, handier to hold, especially on a crowded tram or train. That is all the terms first meant: large page, small page.
Over time the size came to suggest a style, because the small popular papers chased big sales with bold headlines, big pictures, short sharp stories, sport, crime and scandal, while the large papers leaned on politics, business and longer, more serious writing. So "tabloid" picked up its sneer, and "broadsheet" came to stand for the serious press, even though plenty of fine reporting has always appeared in the popular papers too.
Today the labels have come loose from the paper sizes altogether. As I mentioned, even grand old titles have shrunk to the smaller format to suit modern readers, and of course most people now read the news on a screen, where size means nothing at all. So treat the words as a guide to a paper's character, not its measurements. What matters for you, the freelancer, is to study your target. Read it, learn its tone, its story length and its taste, and pitch it the kind of piece it actually runs. A story that is perfect for one can be hopeless for the other.