As the title says, I would like some help to find sources to begin with the study of the revolution movements of the past century because I don't have any idea where is a good place to start.
/u/ThucydidesWasAwesome brings up some important questions, but if youre trying to understand 20th century revolutions, youve got to start right at the beginning. Most revolutions, especially after World War Two, followed the Russian Revolution of 1917. That is the revolution to understand, and I would suggest starting there. There are also a plethera of primary sources out there about the Russian Revolution to start with. Trotsky's' History of the Russian Revolution is a fun place to both get your bearings, and also to understand the motivations behind the revolutionaries. The works of V.I. Lenin are also key. But its also important to remember that many primary accounts of these events are heavily biased, as are many secondary accounts. So its important to remember who the author is, who they support, and how that affects what they say.
That is a pretty broad request. Do you mean you want a suggestion for bibliography on any and all major revolutions in the 20th century? The list would be pretty long.
Or are you asking for a single volume dedicated to revolutions in the 20th century? I'm sure such a thing exists but I have yet to hear of one being recommended too highly. You are likely better off going one by one.
Also, how do you mean 'affected'? In any way? Politically? A revolution tends to have a major impact not just in politics and economics but also culture.
In short, you're casting the net a bit wide.
I can, if you'd like, provide some starting sources to study the Cuban revolution.