The book is a comparative study of revolutionary movements mainly that of French Revolution from 1789-19th century, Russian Revolution of 1917 and Chinese Revolution of 1911 to 1960s Cultural Revolution. Skocpol main thesis is that there are two different types of revolutions mainly political revolutions and social revolutions. Political revolutions transform state structures and political systems but does not extend any further social change. In contrast, social revolutions are revolutions that not only change state structures but also broad social structures and systems including culture, economics, technology, philosophy and other spheres.
For example here is the difference between American Revolution of 1775 and French Revolution of 1789:
The American Revolution of 1775-1791 was a political revolution since there was a change in state structure but no broader systematic change. The Founding Fathers were wealthy merchants, bankers and slave-owners that used their power to secede from the British Empire. The usual peasant or townsperson would not experience anything drastically different from before both socially and economically. Philosophically the Founding Fathers were promoted a liberal conservative doctrine of John Locke which emphasized limited democracy and protection of private property rights.
The French Revolution was a massive overthrow of the Ancien Regime including mass execution of monarchs, aristocrats and feudal ruling class by bourgeoisie, workers and peasants. Philosophically the French Revolution was partially inspired by Jean Jacques Rosseau's more populist conception of liberalism that emphasize mass participation of the citizenry. The French Revolution shattered the conservative doctrine of the divine right of kings and promoted the new philosophies of revolutionary liberalism and nationalism thus inspire future European revolutionaries that monarchs or aristocratic rule is not permanent thus eventually leading to the 1848 Revolutions or other similar revolts.
The French Revolution in contrast had greater social restructuring
https://www.amazon.com/States-Social-Revolutions-Comparative-Analysis/dp/1107569842
https://www.foreignaffairs.com/reviews/capsule-review/1994-11-01/social-revolutions-modern-world
If you haven't read "States and Social Revolutions" you should.
https://www.amazon.com/States-Social-Revolutions-Comparative-Analysis/dp/1107569842