Marx, Engels and Lenin in particular can be very difficult going. One will require an encyclopedia and a dictionary close at hand, but understanding 30 pages of Marx even if it takes several hours, will pay off down the road.

Philosophy

Marx and Engels studied philosophy to dispense with it, before taking up more serious matters in political economy, which is why Marx wrote a book titled "The Poverty of Philosophy."

We recommend starting here:
1. "The Theses on Feuerbach," short and to the point.
2. A lot of people found this useful and accessible to start with also: "Dialectical and Historical Materialism," by J. V. Stalin.
3. Then there is the "Holy Family" and "Economic and Philosophic Manuscripts of 1844," but they can be tough going. So how about, Ludwig Feuerbach and the End of Classical German Philosophy?
4. Next, we suggest you read the very accessible Mao's "Four Essays on Philosophy" including "On Contradiction."
5. After you have conquered all this, a difficult work is Lenin's Materialism and Empirio-Criticism.

Political Economy

Marx also wanted us to dispense with political economy, but there is still no other phrase to describe that area of his work.

We recommend starting here:
1. Value, Price and Profit
2. "Wage Labor and Capital" might be another good starter.
3. Contribution to the Critique of Political Economy.
4. Of course, you already know that some day you do have to read Capital (Das Kapital) (at least vol. 1).
5. You should also get to Lenin's "Imperialism: The Highest Stage of Capitalism," which is still very readable.