1. No Accumulation is just your normal expression. The appropriate aggregated results(sum or count for example) against the respective dimensions
2. Full Accumulation is also called running total. It will take into consideration the current result + all the prior results. For example the result of fifth row(dimension) would be 1st+ 2nd + 3rd + 4th + 5th row results.
3.Step back is like a partial running total. Instead of taking all the previous records it only takes based on whats mentioned in the step back. Lets say step back is 3, then the result of the 5th record would be 3nd+4th+5th
