I'm a complete amateur with signals - help!

[T-Unit]

The best way to learn to create big complex junctions is to start off with small simple ones, learn the basics and apply them to larger ones. For example "Split before merge" (i.e. no bottle necks). There are many more that you will learn including the importance of bridges and tunnels in freeflowing networks.
If you want an efficient network you must remember that the exit of a station is as important (if not more so) than the entrance.