Eh maheshcet,
The L293 is obsolete and the TI SN754410ne has replaced it. Just google that ti part number and the datasheet explains everything and yes it is pin for pin compatible with the L293
The general idea is to generate voltage/ states on 1Y, 2Y, 3Y and 4Y as follow:
1Y 2Y 3Y 4Y
-------------------
1 0 1 0
0 1 1 0
0 1 0 1
0 1 1 0
1 0 1 0 <---- repeat
Each row of state will make the motor turn one step.
for example, say you want to generate the first row of state, according to your diagram, control A and B shouild be logic 0. and so on....