Mike, as said: it is difficult to answer your questions without more information. Automatic Signaling/traffic control is a hobby within the hobby that requires lots of time, careful planning, installation, and additional cost. It is fun, but can be complex for automatic operation and the design of your layout will dictate where and how the signals will operate.
Plan ahead: The worse problem I had was not starting from the beginning with signals in-mind during the original track layout design. When I decided to include signals and began the plan, many changes and additions to the trackage were needed to accommodate smooth traffic flow from block to block. If you already have your layout track down, you will need to study the operations of signals and how they can apply to your layout. You can go prototypical that most visitor operators don't understand or keep it simple with Red=stop, Yellow= caution/slow, Green=go. This is your choice; either way adds loads of fun and will improve traffic flow with several trains running.
I use a Super Chief for a command center and all Digitrax hardware for my block detection and signal drivers. The wiring is actually fairly simple for block detection with one wire from the block detection board per block and the common rail wire of all blocks in that power district back to your command module/track power. The detection rail will be gapped at each end of the block.
The brains for my operation is handled by Railroad and Company software.
http://www.freiwald.com/
This hardware is very user friendly and there is nothing it can't do; no programming knowledge needed. The downside is it can be expensive ranging in price: $129-$389-$584. (I suggest the upgradable $389 Silver for a beginner) This software can even run your trains automatically and provide exact and timed stops along the way(I use this for my passenger trains and run the freights manually). All trains can be monitored by location and auto-emergency stopped if needed, i.e. no pasture meets

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I would like to suggest you visit the Digitrax site and download the manuals for the BDL168. This is the block detection board and will give you a lot of information about how to layout your blocks and how it all works. The RR&Co site also has a lot of info and sample diagrams.
Lots to think about and plan, but I assure you that if you are willing to put in the time and money, signals will provide you with loads of realism and fun.

