Short answers, pulled from the story.
A steamship, often called a steamer, is a steam-powered vessel, typically ocean-faring and seaworthy, propelled by one or more steam engines that turn propellers or paddlewheels. The first steamships came into practical use during the early 19th century.
No. "SS" stands for screw steamer, indicating a ship driven by a propeller or screw, while "PS" stands for paddle steamer. As paddle steamers became less common, many people incorrectly assumed "SS" meant "steamship".
The American ship Savannah is credited as the first steamship to cross the Atlantic between North America and Europe, leaving Savannah, Georgia, on the 22nd of May 1819 and arriving in Liverpool on the 20th of June 1819. She was a hybrid, using her steam engine for only part of the voyage, with estimates of total steam use ranging from 8 to 80 hours.
Screw propellers replaced paddlewheels because the propeller's efficiency stayed consistent regardless of the depth at which it operated, unlike the paddle-wheel, which lost performance when added weight submerged it too far. Being smaller, fully submerged, and lighter, the propeller was also far less prone to damage.
The opening of the Suez Canal in 1869 cut about 3250 nmi off the route from China to London, a saving available to steamers but not to sailing vessels, for which towing was difficult and expensive. Steamships were in high demand for the 1870 tea season, and in 1871-45 ships were built in Clyde shipyards alone for Far Eastern trade.
Steamships declined after the early 1950s because marine diesel engines had matured into a cheaper, more space-efficient alternative with far better thermal efficiency and less need for supervision, boilers, or a water supply. No commercial ocean-going steamers with reciprocating engines have been built since the 1960s.