There are three bit-type tables you need to understand. All are addressed in the same manner. Inputs from hardware devices are in the "I" table. Hardware outputs are stored in the "Q" table. Internal memory is found in the "M" table.
For each type, the address format is Ix.y, Qx.y, and Mx.y, where "x" is the byte number and "y" is the bit number (0 - 7). For example, the first I/O card in the PLC rack typically has addresses I0.0, I0.1, I0.2...I0.7, I1.0, I1.1,..I1.7, for a 16-point input card.