GCode

The reference doc for 3d printing gcode is here: http://reprap.org/wiki/G-code
I keep going back here all the time, a few I can remember off-by-heart though.
Unfortunately there are documentation issues with g-codes, while each normally does roughly what is described, each printer firmware has its own quirks, which are not well published. But most of the common ones are fairly well defined & predictable these days.

As per original Gcode, All the chunks of the command are a letter followed by a number (yes, some rare exceptions like the "display message" command), so these are T0 (zero) and P0 (zero).

P is usually used for generic Parameters - if a command only takes one, it's often P or S (a loose convention of sorts)
T is a special Tool select command - T0 means you're selecting extruder 0. The S parameter here is actually the temperature!

Note that the M109 command is not setting the bed temp - it's setting the extruder temp, then waiting for that temperature to be reached (110C). Bed temperature is typically set with M140, set-and-wait with M190.