components base address and offsets

I know how to get the base address of each component in a NIOS II system "Qsys" or the "system.h" file.

What I dont understand is what is the offset and how to get it.

for example component's base address starts at 0x0000 and ends at 0x0001, does this represents a 32bits line and the offset is the index of the byte to read ?

If that the case, how do I know how the bytes are mapped to the component pins ? ( writedata is the first or the second ... ?)