The forearms consist of many different muscles and the exact number depends on the anatomy book you are reading! Frequently, the forearms are broken down into three main parts: the brachioradialis, the wrist flexors, and the pronator teres.
The brachioradialis originates at the humerus and inserts into the radius. The muscle has two functions, elbow flexion (curling movements), and forearm pronation (twisting the forearm until your palm faces the floor).
The wrist flexors are numerous and complex. For the purpose of strengthening and building the wrist flexors, you only need to know the general functions of these muscles.
Each of the wrist flexors either acts on the wrist joint or on the fingers themselves. As its name suggests, the wrist and finger flexors flex the wrist and fingers. Basically, the wrist flexor group is active every time you use your fingers to pick something up.
The pronator teres is visible near the elbow. This muscle originates at the humerus and ulna, and inserts into the radius. Together with the brachioradialis, the pronator teres pronates the forearm and flexes the elbow.