Short answers, pulled from the story.
The Battle of Guam began on the 8th of December 1941 when Japanese aircraft attacked Marine barracks and the Piti Navy Yard. The main invasion landing occurred early morning on the 10th of December 1941 at Dungcas Beach north of Agana.
Major General George McMillin served as governor of Guam and commander of the naval base from 1899 onwards until his surrender in 1941. He ordered Marines to surrender at 05:45 on the 10th of December 1941 after token resistance against the South Seas Detachment.
Thirteen American civilians died by Japanese hands during the battle while local Chamorros protected Radioman First Class George Ray Tweed for two years and seven months. Chamorro suspects were tortured and beheaded by Japanese forces who knew an unknown American could not hide without help.
The South Seas Detachment included the 144th Infantry Regiment and other units totaling 4,886 men before sailing for Chichi-jima in November 1941. Approximately 5,500 men under Major General Tomitarō Horii made separate landings at Tumon Bay, southwest coast near Merizo, and eastern shore at Talofofo Bay.
Guam received a Category F defense rating in 1941 that ruled out construction of new defenses or practical reinforcement efforts. The United States government determined it would be impossible to defend the island if attacked due to its distance from the Philippines and lack of strategic utility beyond refueling points.