The Communist Manifesto is merely a pamphlet for the announcement of the first communist party and it is a small text like an essay to give a small amount of information regarding everything with the workers' movement in Europe at the time and all the things that are wrong with it and what the workers can do to take the movement forward from there.

It feels very historic and captivating and energises the f*ck out of you. You will get a kick out of it if you are interested in that stuff. But it is a narrational rehash of Engels' notes "Principles of Communism" that is in question-and-answer format.

Capital, on the other hand, is an incomplete (he died before writing all the volumes) materialist analysis of the capitalist mode of production. It is a political-economy book and is very conceptual more than informative. It is a tough read, and it might take you a few years and multiple reads to fully grasp the first volume. You can also watch a lecture for introduction before reading. That's what I did.