You as a consumer can place a market order (mo) or limit order (lo).
It is very dangerous placing a market order, unless you're in real-time, because the 15-20 delay in what you see may not be accurate. Say you see $1.00/share then go market. Real time might be $1.10!
Limit orders tell the MMs you want to buy or sell a certain amount at a limit, say $0.99. If the amount is large enough an MM may drop their ask price to meet your price.
Sometimes this is why you see bid/ask prices which are not the same as the last transaction price.