First, if you're looking for an answer to "what does a code mean", your best bet is to just Google it. Find out what the code is telling you. This will give you a list of things it might be. You can start your troubleshooting from there.
Now, for what do these things mean ... (these should hold true for most codes, but double check to make sure)
Malfunction - I think this is fairly easy from my standpoint. It means the sensor isn't working. It's either dead, isn't sending a signal, or isn't sending the proper signal.
Range/Performance - The range has to do for the total output of the sensor. In most cases there's going to be a specific voltage range the ECU is expecting. If it isn't performing correctly and giving some kind of weird range which the ECU doesn't understand (ie: it should be .5vdc to 1vdc and is giving .4vdc to 3vdc), the ECU is going to question the sensor and throw the code (this is a crude example). As far as performance, if the ECU is expecting a sensor to behave in a certain way, and yet isn't, then it might throw the code because of this.
Low/High Input - (Throwing these together because it makes sense this way.) If the ECU is expecting the signal from a sensor to only go down to .5vdc and yet is down at .25vdc (or even zero), it might throw this code. The voltage output of the sensor is below the voltage expected for the sensor. Conversely, if output is too high, it would throw the other. In the case of a MAP sensor, it probably means replacement. If you are looking at a throttle pedal, it probably only needs a recalibration.
Circuit Intermittent - To me, this is pretty explanatory, but basically, the signal coming back from the sensor is erratic and isn't continuous, so the ECU calls it out.
You can't expect yourself to know everything listed as an OBDII trouble code, so don't try. All of this stuff, to include explanation and what/how to troubleshoot can pretty easily be found on the internet, so don't limit yourself.