Short answers, pulled from the story.
The conflict began after shots were fired on the 5th of December 1934 during a confrontation at the Welwel oasis between Ethiopian and Italian forces. This incident triggered the Abyssinia Crisis at the League of Nations following an earlier dispute over boundary commission activities in November 1934.
Marshal Emilio De Bono crossed the Mareb River advancing into Ethiopia without declaring war at 5:00 am on the 3rd of October 1935. Two hundred thousand soldiers of the Italian Army attacked from Eritrea while a minor force under General Rodolfo Graziani moved from Italian Somaliland.
A 2017 history estimated that 19,200 people were killed representing 20% of Addis Ababas population during the Yekatit 12 massacre. Estimates vary widely with Ethiopian sources claiming 30,000 deaths while Italian sources claimed only hundreds died.
Haile Selassie fled Ethiopia after Italian forces defeated his main army at the Battle of Maychew on the 31st of March 1936 causing the army to disintegrate. On the 2nd of May Selassie boarded a train carrying gold from the Ethiopian Central Bank fleeing to Djibouti then onward to exile in the United Kingdom.
Haile Selassie spoke at the League of Nations introducing himself as His Imperial Majesty Emperor of Ethiopia and denounced aggression against his country. Jeering Italian journalists began yelling insults before being expelled though the League voted to end sanctions imposed against Italy by the 15th of July 1936.