Here is what you need to know before the hearings are gaveled in.

Mr. Trump will be accused of bribery and abusing his power.

At its simplest, Democrats’ contention is that Mr. Trump abused the power of the presidency to enlist a foreign power to benefit his re-election campaign. That was the central charge of an anonymous C.I.A. whistle-blower whose complaint about the president’s dealings with Ukraine prompted Speaker Nancy Pelosi to begin the impeachment inquiry.

But the president’s critics have begun sharpening their language to invoke terms like bribery, extortion and coercion against Mr. Trump, echoing the language in the Constitution that lays out offenses worthy of impeachment: “treason, bribery, or other high crimes and misdemeanors.”

The centerpiece of their case is a reconstructed transcript released by the White House of a July phone call between Mr. Trump and President Volodymyr Zelensky of Ukraine. In it, Mr. Trump asked Mr. Zelensky, Ukraine’s newly elected leader, to “do us a favor” and investigate former Vice President Joseph R. Biden Jr. and his son Hunter Biden as well as a conspiracy theory that holds that Ukraine, not Russia, interfered in the 2016 election to help Democrats, not Mr. Trump.

Democrats will use the hearings to explain their case to Americans, while Republicans will try to poke holes.