A firm can be defined as any business entity that operates for profit. It can refer to a variety of company structures, such as single proprietorships and corporations. A firm can be a physical product-oriented business, such as a consumer goods store.
In tha labor market, firms act as buyers of labor services. The labor bought in this market is then used along with other inputs to produce goods and services. These goods and services are then sold by the firms in the goods market to earn profits.
So, firms are sellers in goods market but buyers in labor market.