First of all, there is no such thing as Luxemburgism, Rosa Luxemburg was just a regular Marxist.
She is known for her idea of revolutionary social democracy as she believed the dictatorship of the proletariat a true form of democracy, this could take form in the shape of worker's councils and she opposed Lenin's methods which as a result influenced (Left-) Council Communism after on.
She also played an important role influencing Marxist-Humanism and Marxist-Feminism.
In this book, Luxemburg argues that reformist political parties and the expansion of social democracy—while important to the proletariat's development of class consciousness— cannot create a socialist society as Eduard Bernstein, among others, argued. Instead, she argues from a historical materialist perspective that capitalism is economically unsustainable and will eventually collapse and that a revolution is necessary to transform capitalism into socialism
In this lengthy book Luxemburg expands on the ideas of capital accumulation
Luxemburg is know for her opposition to Lenin, in which they disagreed about how to organise the (vanguard) party and how much role should the party play in the revolution, Moreover, according to her Lenin was abandoning Marxism in favour of Blanquism; According to her the core idea of Marx "The emancipation of the working classes must be conquered by the working classes themselves" was being abandoned in favour of an elitists ruling until the people can rule which was proposed by Louis Auguste Blanqui.
She explains in in her works : Organisational Questions of the Russian Social Democracy and the Russian Revolution
Because of this opposition she is considered a "Libertarian Marxist" however like any other Marxist she believed that Libertarian / Authoritarian distinction is too vague (which is explained by Engels in "On authority") and that the revolution is inherently Authoritarian because the proletariat would enforce their authority to the bourgeoisie.
"All this resistance must be broken step by step, with an iron fist and ruthless energy. The violence of the bourgeois counterrevolution must be confronted with the revolutionary violence of the proletariat. Against the attacks, insinuations, and rumors of the bourgeoisie must stand the inflexible clarity of purpose, vigilance, and ever ready activity of the proletarian mass. Against the threatened dangers of the counter-revolution, the arming of the people and disarming of the ruling classes. Against the parliamentary obstructionist maneuvers of the bourgeoisie, the active organization of the mass of workers and soldiers. Against the omnipresence, the thousand means of power of bourgeois society, the concentrated, compact, and fully developed power of the working class..."
"Such arming of the solid mass of laboring people with all political power for the tasks of the revolution-that is the dictatorship of the proletariat and therefore true democracy. Not where the wage slave sits next to the capitalist, the rural proletarian next to the Junker in fraudulent equality to engage in parliamentary debate over questions of life or death, but where the million-headed proletarian mass seizes the entire power of the state in its calloused fist – like the god Thor his hammer – using it to smash the head of the ruling classes: that alone is democracy, that alone is not a betrayal of the people."