42 USC § 1983 is a statute, a law enacted by Congress. The law allows a person whose Constitutional rights were violated by government officials to sue in federal court. The defendant in the case must be someone acting on behalf of a state or local government. A plaintiff can also sue a local government, such as a city, for violating his constitutional rights.
Congress passed 42 USC § 1983 because of a concern after the United States Civil War that southern states deprived black people of their Constitutional rights. 42 USC §1983 empowers victims to sue state officials, and those acting on their behalf.
A Bivens Action is different because the defendant in a Bivens Action is alleged to be acting on behalf of the federal government, not a state government. The Supreme Court, in Bivens v. Six Unknown Agents of the Federal Bureau of Narcotics, 403 U.S. 388 (1971), held that plaintiffs whose Constitutional rights were violated by persons acting on behalf of the federal government (may) have an implied right to sue federal officials in federal court. The plaintiff in that case was named Warren Bivens so now we call these types of cases “Bivens Actions”.
Learn more about a 2017 Supreme Court case, Ziglar v. Abbasi which discusses the scope of Bivens actions and the separation of powers:
Below is an older video on Bivens Actions: