I had heard that too that there must be a buyer an

I had heard that too that there must be a buyer and seller for a stock trade to occur.  What, then, is the place of the market maker?  If someone wants to sell a 1000 shares and there are buyers for 500 shares, does the market maker buy the other 500 shares and put them in his inventory to sell when he chooses?  Does this explain how there can be days where the buys outnumber the sells and yet the price goes up very little or even falls?  Because the MM can choose to sell part of his inventory at any price he chooses and manipulate the price of the stock?  I don't honestly know, but it sure is irritating to see more buys than sells and the price hardly move at all or go down.  Trying to learn and get better.  My best to you,   Jim