Short answers, pulled from the story.
The Battle of Heilsberg took place on the 10th of June 1807, near the town of Heilsberg, known today as Lidzbark Warmiński in Poland. An undocumented truce ended hostilities on the 11th of June, after which Bennigsen withdrew his army on the night of the 12th.
Marshal Joachim Murat led the French troops at the start of the battle, initiating the attack before Napoleon Bonaparte arrived. Napoleon reached the battlefield at 6 pm and took joint command alongside Jean Lannes' corps. Marshal Nicolas Jean-de-Dieu Soult and Marshal Louis-Alexandre Berthier were also present among the notable French officers.
General Levin August von Bennigsen commanded the Russian forces, but illness forced him to rely on Lieutenant General Andrey Gorchakov, who took over general command for the final hours of the battle. Bennigsen remained on his horse despite falling unconscious several times during the fighting.
French losses were estimated at around 12,000 men total. The French army claimed 1,398 killed, 10,059 wounded, and 864 captured. The bulk of the losses fell on Soult's IV Corps, which suffered 8,286 casualties. General François Xavier Roussel, Chief of Staff of the Imperial Guard, was killed, and three French units lost their eagles.
The Battle of Heilsberg ended in a tactical draw and is recognized as strategically inconclusive. Neither side gained significant ground, and the battle is generally described as a successful Russo-Prussian rearguard action. Napoleon never realized he faced Bennigsen's entire army during the engagement.
The Battle of Heilsberg was fought four days before the Battle of Friedland on the 14th of June 1807. Friedland proved decisive: Napoleon defeated Bennigsen there and ended the War of the Fourth Coalition, which concluded with the Treaty of Tilsit.