Ladder diagrams are graphical language and Instruction list is different, Allen Bradley Micrologix software uses Instruction list as the programming language. Basic ladder logic instruction is converted to Instruction list to understand the Instruction list.
Here in the above two ladder logic, there is only one input which is A, and what it is, is the output X. On the instruction list side, it says LD A then in the next line ST X. LD A means A is loaded and which is in the top of the stack now. As A is the output ST X mean, the value at the top of the stack is the output, Now it is A.
In the next ladder logic, the change is that input is Not A. Which is replaced with LDN A in instruction list program. LDN A means load not A.
Now, this is the example with two inputs A & B, First A and B are loaded, then ANB which means B AND A. A is not mentioned because which is already in the stack. After B AND A is done, now the result is in the stack which is stored as output x(ST X).
OR instruction is added to the program. The program above is ( A OR B ) AND C. It is also easy to understand from the instruction list program, A and B are loaded and they are ORed with the instruction ORB. Then C is loaded and ANDed with the B using the instruction ANB because C is on the stack now. Doing the AND operation register B is loaded with ( A OR B ) AND C.
Same as the above program but the OR latch is moved under B. Here all the input are loaded first. At last C will be at the top of the stack and C OR B, the result will be stored in B, then
newB AND A. Operation is done in opposite direction.