About Signal Processors:
Just what is a "signal processor," anyway? In a sense, everything can be “you send a signal in one end, and it comes out the other end different than it was when it came in.” But what we're talking about here is the range of useful tools, usually in handy rack-mount packages, that give your performance or recording a final polish of the rough edges (or rough up the polished edges, if that's what you're after). They are all important parts of your final sound, and well worth spending a little time learning about.
Generally speaking, there are three basic classes of signal processors; time-based, frequency-based and dynamics processors. Time-based processors include reverbs, delays, choruses and flangers. Frequency-based effects are largely EQs and filters, with compressors and limiters making up the dynamics processors. There are analog and digital versions of all of these, and which ones you need will very much depend on the rest of your gear and what you want the final audio to sound like.
In addition to the basic types of effects, there is a wide variety of connectors available, ranging from consumer-level phono (sometimes called RCA) plugs to balanced XLR connections for analog connections. For the most part, balanced connections interface better with professional gear, being designed for less noise and the ability to drive longer cable runs without excessive signal loss (though it's always a good idea to keep cable runs as short as possible. Just because your connection can drive a signal 30 meters doesn't mean you should have 100' of cable coiled behind your equipment rack). Digital equipment adds a whole new category of connector, with optical connectors a popular option for multi-channel digital connections. Just remember that adapters and converters tend to mess with your signal integrity, so make sure that your connections match as much as possible.
Spend time auditioning processors and don't be afraid to ask knowledgeable people, like the Guitar Center Pro Audio staff, for guidance. There's a lot of cool stuff out there, and they can help you find just the right processors for your system.