I'm not really familiar with the MarkII, but just to start you out, it looks like they have a prototyping board already availablehttp://www.junun.org/MarkIII/Info.jsp?item=4
-In general a letter with a number after it are general I/Os (input/outputs) (often just digital, but not always)
-PWM are pulse with modulators which are good for servos and low energy loss driving source (ie you can use it to "pulse" a voltage rather than using a resistor to bring down a voltage.
-LineR, C, L sounds like a digital input for following a line, one for the right, center left respectively
-Vss is power source usually >6V
-V+ a regulated power usually 5V
-Vdd is gound
-Int is an interrupt (tells the processor "Hey! pay attention to this"
-SCL and SDA are for communications (Serial CLock and DAta)
-TX and RX are also for communications ie UART which can be converted to RS232
-can't say much for the rest
it's not everything, but hope its a start
A general manual can be found:http://www.junun.org/MarkIII/Manual/index.jsp
a forum to ask Mark III specific questions:http://tech.groups.yahoo.com/group/MiniSumoMarkIII/