The Engineer controlled the engine and drove the train in addition to seeing that wheels and other lubrication points were kept oiled. In photos, the man in the puffy striped hat carrying a large oil can is the engineer.
The Fireman was responsible for coal and water. He was the stoker who shoveled coal into the boiler and kept the supply of coal available from the tender. He was also responsible for taking on water which steam engines used in large quantities. Thus, trains had to stop every few miles and take on water. A fold-up spout located alongside the tracks, typically at or near the station would lower to provide the needed water while the train was stopped. The Fireman oversaw the taking on of water and, when necessary, coal.
The Brakeman oversaw the switching of cars in the rail yard and when necessary, got off the train to throw switches by hand (such as when backing into a siding or executing a turnaround). In a pinch, he and the Engineer might help load or unload local freight.
And finally, there was the Conductor, the man in the pillbox hat with the partial brim who yelled “All Aboard!” and later came wandering through the passenger cars calling out “Tickets please!” His job was much more than that, however. The Conductor was the supervisor responsible for the overall well-being of the train. He kept all records of both passengers and freight and typically kept a small office (desk and chair) in the caboose where he did his record keeping. Applicants were, and are, required to pass an examination to become conductors.
A common non-train railroad employee was the Station Master or Depot Agent who sold tickets, kept records on freight and oversaw the station/depot. Early station masters and their families lived on site. As you drive past the Morehead freight station, notice the second floor. This was the residence of the Station Master and his family. All railroad business was conducted downstairs including the sale of tickets and the temporary storage of outgoing and incoming freight. Later the upstairs was used as overnight facilities (bunks etc.) for train crews overnighting in Morehead.
Mail was the responsibility of the Postal Service. When no stop was scheduled at a particular station, a mailbag was hung on a mail crane (a support which held the bag in a position to be hooked by an arm which swung out from the mail car). The train would rumble through and the mailbag would be snared and then swung into the mail car where the mail was sorted in route. Only Postal Service employees were allowed in the mail car and, yes, they were armed (dating back to the days of the great train robberies).