1. The M-C-M diagram explains how capitalists make and grow their wealth through three steps:  

M: It all starts with money. The capitalists would put their money to work to invest in the kind of business that would allow them to buy everything they needed to produce goods for selling.

C: It is with that money that workers are employed and the materials and machines are bought to make up the products. These products are what they sell in the market.

M: And so, when the products are manufactured, they are sold for a price more than the cost of making them. The balance between the selling price and cost becomes the profit.  

2. Following this cycle, capitalists tend to reinvest their profits for the growth of their businesses. They might create or develop new products expand their areas of operation or upgrade their technology so that they could manufacture the goods more efficiently. 

This is associated, to a great extent, with how they pay their workers. Usually, wages paid to workers are less than the value of what they generate such that what is left is profit for the capitalists. This is how capitalists keep accumulating wealth over time.

To put it once more, the M-C-M process cycle comprises turning the initial money into goods that yield more money and reinvesting that profit to generate further wealth accumulation. This cycle is really important in understanding how wealth builds up in a capitalist economy.