Similar to the British system, Article One of the United States Constitution gives the House of Representatives the sole power of impeachment and the Senate the sole power to try impeachments of officers of the U.S. federal government. It's the Senate that acts as the 'grand jury', not the House.
Process
At the federal level, the impeachment process is a two-step procedure. The House of Representatives must first pass, by a simple majority of those present and voting, articles of impeachment, which constitute the formal allegation or allegations. Upon passage, the defendant has been "impeached". Next, the Senate tries the accused. In the case of the impeachment of a president, the Chief Justice of the United States presides over the proceedings. For the impeachment of any other official, the Constitution is silent on who shall preside, suggesting that this role falls to the Senate's usual presiding officer, the President of the Senate who is also the Vice President of the United States.
In theory at least, as President of the Senate, the Vice President of the United States could preside over their own impeachment, although legal theories suggest that allowing a defendant to be the judge in their own case would be a blatant conflict of interest. If the Vice President did not preside over an impeachment (of anyone besides the President), the duties would fall to the President pro tempore of the Senate.
To convict an accused, "the concurrence of two thirds of the members present" is required.[35] Conviction removes the defendant from office. Following conviction, the Senate may vote to further punish the individual by barring him or her from holding future federal office, elected or appointed. Conviction by the Senate does not bar criminal prosecution. Even after an accused has left office, it is possible to disqualify the person from future office or from certain emoluments of his prior office (such as a pension). If there is no charge for which a two-thirds majority of the senators present vote "guilty", the defendant is acquitted and no punishment is imposed.