A market taker is a participant of the market, that is agreeing with the currently listed prices on the order book and wishes to fill his trade immediately. If the highest selling price and the lowest buying price is okay for you and you settle a trade, you become a market taker.
A market maker places the orders with prices that are different from the current market price. Usually, a market maker will try and sell for higher price and buy for lower price. If you make an order with a price that is different from the market price, you are a market maker. Market maker’s trades are not filled immediately, they usually appear in the order book and are executed when a market taker finds maker’s price satisfactory.