The February Revolution (March in the Gregorian calendar) was the first stage of the Russian Revolution of 1917. The result was the forced abdication on March 1st (O.S.), of Tsar Nicholas II and the end of the Romanov dynasty and the monarchy. And chaos.
This revolution appeared to break out spontaneously, 22 - 25 February (O.S.) without any real leadership or formal planning, brought on by constant political agitation by the Liberal-Left parties, by endless strikes, and in particular by food supplies being unable to reach the capital after the worst winter in memory. Food was already in short supply due to the peasants being drafted into the army and many harvests rotting ungathered in the fields as a result. What food there was appeared to be going firstly to the army at the Front. The tensions which had for so long been building up finally exploded into a revolution, and Petrograd (St. Petersburg prior to the war) became the initial focal point of activity. The garrison in the city was made up largely of inexperienced conscripts who were poorly trained and psychologically ill-prepared to address the riots taking place. Many deserted and others joined the rioters.
A Russian Provisional Government, liberal and socialist in its make-up, was formed under Prince Georgy Lvov. The United States of America was the first world power to recognise the new regime, on 9/22 March. Prince Lvov was later succeeded by Alexander Kerensky after the tumult of the July Days. This government said it wanted to instigate political reform, broaden the executive, the constituent assembly (Duma), and widen the franchise. It's fatal mistake was to pledge that it would continue Russia's involvement in The Great War until "final victory".
An illustration of just how large Russia was is that it took some years for eastern parts of the country to realise that a revolution had actually taken place.
The February Revolution was followed eight months later by the October Revolution, bringing about Bolshevik rule and a total change in Russia's social structure, paving the way for the USSR and Communism.