Short answers, pulled from the story.
Russia entered World War I after Tsar Nicholas II ordered general mobilization on the 30th of July 1914 to deter Austria-Hungary from invading Serbia. This decision followed a period of indecision and occurred before Germany declared a state of imminent war.
Russia joined World War I due to rising Pan-Slavism, pressure from public opinion, and Foreign Minister Sergei Sazonov's warning that failing to support Serbia risked revolution. The government also sought to capture Constantinople and control the Dardanelles Straits to gain access to the Mediterranean Sea.
Russian military failures were caused by incompetent leadership where Grand dukes ascended to high command positions despite lacking necessary skills. War Minister Vladimir Sukhomlinov harbored animosity toward field commanders, creating internal strife that plagued the High Command before major battles began.
Russia faced severe logistical challenges because it possessed ten times less railway track per square kilometer than Germany. Soldiers traveled an average distance of 1,290 kilometers to reach front lines while ports like Vladivostok lay over 6,400 kilometers away and froze solid during winter months.
Austria-Hungary officially declared war on Serbia on the 28th of July 1914. This declaration triggered immediate attacks against German territory and led to the Battle of Tannenberg which annihilated the entire Russian Second Army.