Difference between in marge sort and bubble sort ?

Bubble sort compares two adjacent element and put them in order, then later of two sorted element is again compared to adjacent one, go through whole list and process is repeated unless every element is in order while in merge sort, each element is treated as full list and then its merged with each other, creating multiple sorted list and then again those multiple list are merged after sorting until the final single sorted list is obtained.

Best method to understand these is to see some graphical presentation and then test them in your preferred language. Just search google and you may get some good references.