What are Perfectly Competitive Markets?

Prices are determined by supply and demand in a market with perfect competition. Because no single business has enough market control in a completely competitive market, all firms are price takers. Firms in a completely competitive market have a limited market share, unlike monopolistic markets. Entry barriers are minimal, and businesses may readily enter and depart the market.
A completely competitive market, in contrast to a monopolistic market, has numerous buyers and sellers, and customers have the freedom to select where they acquire their goods and services.
Companies make just enough money to stay afloat, but no more. If they made too much money, other businesses would enter the market and reduce earnings. Perfect competition, as previously said, is a theoretical concept. As a result, real-life instances of perfect competition are hard to come by.

So many sellers and so many buyers no one has any control over price. A tiny increase in price above the market level causes sales to vanish, a tiny decrease below the market level causes sales to overwhelm the supplier.

Perfect competition is an intellectual model to facilitate understanding and predict effects, there is no assumption that it exists. See point-mass in physics: all the mass of an object is concentrated in a single infinitesimal point - useful for understanding Newtonian physics but no such thing ever existed. However, both point-mass and perfect competition can be approached and the real world approximates some of the characteristics.