Short answers, pulled from the story.
Lenin wrote the book in Zürich during January through June 1916 and sent it to a Petrograd publisher that same year. It was published in mid-1917 by Zhizn i Znaniye Publishers in Petrograd, with a preface dated the 26th of April by Lenin.
Lenin argues that capitalism had reached an advanced stage characterized by monopolies formed from the merger of banking and industrial capital, producing a financial oligarchy. This finance capital drives the export of investment to underdeveloped countries, requiring colonial exploitation and inevitably producing wars between imperial powers over the redivision of territory.
Lenin synthesized two major prior works: Imperialism: A Study (1902) by the English economist John A. Hobson, and Finance Capital (1910) by the Austrian Marxist Rudolf Hilferding. He also built on Karl Marx's political economy from Das Kapital (1867) and directed his argument against Karl Kautsky's theory of ultra-imperialism, proposed in 1914.
Lenin sent the manuscript to Parus, a Petrograd publishing house set up by the writer Maxim Gorky. It was announced in Gorky's magazine Letopis and published by Zhizn i Znaniye Publishers. Gorky placed it outside the regular series of war surveys edited by Marxist historian Mikhail Pokrovsky.
In the preface to the French and German editions, Lenin proposed that revolt against the capitalist global system would come from the "thousand million people" of the colonies and semi-colonies rather than from the urban workers of Western Europe. He cited the October Revolution of 1917 in Tsarist Russia as evidence that revolution could begin in underdeveloped rather than advanced industrial countries.
Kwame Nkrumah took direct inspiration from Lenin's text for his analysis of neocolonialism. His book, Neo-Colonialism, the Last Stage of Imperialism, alluded explicitly to Lenin's title, arguing that formal political independence had not ended the underlying colonial economic relationships Lenin had described.