In regular merge sort array is recursively get divide until single element is obtained. From there we pick the each element and sort them(which is kinda obvious single element is already sorted). Then we obtain two elements arraya and compare and merge them.
2-way merge sort we take 2 elements at a time instead of 1 from the point we have divided the array to singleton element.
8-7-6-5-4-3-2-1
{8,7}-{6,5}-{4,3}-{2,1}// see pick two elements at a time now sort them
{7,8}-{5,6}-{3,4}-{1,2} // again pick two sorted elements and merge them then sort
{7,8,5,6}-{3,4,1,2}// sort them
{5,6,7,8}-{1,2,3,4} // again we obtain sorted elements now again merge
{5,6,7,8,1,2,3,4} // now sort them again
{1,2,3,4,5,6,7,8} // sorted using 2-way merge sort.
Hope you get the difference.
It is just same after second step of regular merge sort.
