This is my personal recommended reading list for anyone interested in leftism. This is from a Marxist-Leninist perspective.
PART ONE: The Basics of Communism
- Why Socialism by Albert Einstein (https://monthlyreview.org/2009/05/01/why-socialism)
- The Principles of Communism by Friedrich Engels (https://www.marxists.org/archive/marx/works/1847/11/prin-com.htm)
- Manifesto of the Communist Party by Karl Marx & Friedrich Engels (https://www.marxists.org/archive/marx/works/1848/communist-manifesto/)
- Socialism: Utopian and Scientific by Friedrich Engels (https://www.marxists.org/archive/marx/works/1880/soc-utop/index.htm)
- The State and Revolution by V.I. Lenin (https://www.marxists.org/archive/lenin/works/1917/staterev/)
PART TWO: Critiques of Capitalism/Imperialism
- Wage Labour and Capital by Karl Marx (https://www.marxists.org/archive/marx/works/download/pdf/wage-labour-capital.pdf)
- Imperialism: The Highest Stage of Capitalism by V.I. Lenin (https://www.marxists.org/archive/lenin/works/1916/imp-hsc/)
- Capital: A Critique of Political Economy - Vol. 1 by Karl Marx (https://www.marxists.org/archive/marx/works/1867-c1/)
PART THREE: Dialectical Materialism
- Introduction to Marxist Dialectics by Thomas Weston (http://marxistphilosophy.org/Intro/DialIntro.pdf)
- The Origin of the Family, Private Property, and the State by Friedrich Engels (https://www.marxists.org/archive/marx/works/1884/origin-family/index.htm)
- Dialectical and Historical Materialism by J.V. Stalin (https://www.marxists.org/reference/archive/stalin/works/1938/09.htm)
- Anti-Dรผhring by Friedrich Engels (https://www.marxists.org/archive/marx/works/1877/anti-duhring/)
- Dialectical Materialism by Mao Zedong (https://www.marxists.org/reference/archive/mao/selected-works/volume-6/mswv6_30.htm)
PART FOUR: Anti-Revisionism
- Critique of the Gotha Programme by Karl Marx (https://www.marxists.org/archive/marx/works/1875/gotha/)
- "Left-Wing" Communism: An Infantile Disorder by V.I. Lenin (https://www.marxists.org/archive/lenin/works/1920/lwc/)
PART FIVE: Bolshevism and Soviet Communism
- The Foundations of Leninism by J.V. Stalin (https://www.marxists.org/reference/archive/stalin/works/1924/foundations-leninism/)
- Mastering Bolshevism by J.V. Stalin (http://www.marx2mao.com/Stalin/MB37.html)
- Communist League by J.V. Stalin (https://www.marxists.org/reference/archive/stalin/works/1928/05/16.htm)
PART SIX: Mao Tse-Tung Thought
- "The Little Red Book" by Mao Zedong (https://www.marxists.org/ebooks/mao/Quotations_from_Chairman_Mao_Tse-tung.pdf)
- On Practice by Mao Zedong (https://www.marxists.org/reference/archive/mao/selected-works/volume-1/mswv1_16.htm)
- On Protracted War by Mao Zedong (https://www.marxists.org/reference/archive/mao/selected-works/volume-2/mswv2_09.htm)
- Counter-revolutionaries by Mao Zedong (https://www.marxists.org/reference/archive/mao/selected-works/volume-5/mswv5_13.htm)
I also recommend reading:
Blackshirts and Reds by Michael Parenti
Democracy at Work: A Cure for Capitalism by Richard D. Wolff