Are you still reading Lenin? How's it going – did it get any easier?
I have stop reading Lenin temporarily bc his works are above my level of understanding
That's acceptable! I've had to do the same and I still do now and again. I got completely lost with Marx at first. Even the Communist Manifesto was a bit too complex. I read it and thought I understood, but I later realised that I had misunderstood most of it. So I read three or four biographies of Marx and some easy introductions to Marxism before going back to Marx and the other founders. The background knowledge from the biographies helped a lot (although now I think that some of the biographers misunderstood some of the basics, too!). Better to read comprehensible texts easily then go back to the more difficult texts later.
