Going off what you have said Mansen, regarding the amount of cash available at the start, it may be best to just use road transport to start with and get the industries producing, so that more funds are available to get at least a few rail lines in place. Best not to be too ambitious early on in the game I suppose.
Anyway Steve seems to be on track (excuse the pun) with his signalling explanations and it will no doubt help others new to these games to get trains running to the best advantage on single line workings.