A lot of the contradictions can be boiled down pretty simply. Essentially, capitalism needs to do a thing (or, many things) to survive, but the process of doing those things leads to the collapse of that thing.

Just consider basic middle school economics for an easy example. For capitalism to function, widgets need to be sold, and someone needs to buy those widgets. Capitalism demands that those widgets be sold at the absolutely highest profit margins possible. This means cutting costs wherever possible, leading to lower quality widgets that need to be bought more often AND lower paid employees that can buy less widgets. Now imagine a basic society where the entire working class is making that same widget. As wages to make that widget goes down, less widgets can be bought. In order for this system to sustain itself, costs must continue to be cut. Workers are paid less, less widgets can be bought, and we're now in a negative feedback loop. Eventually nobody can afford to buy widgets, so the factory owner cannot buy materials to buy more widgets, and the entire system collapses.

All of the contradictions are like this. A thing happens so that another thing happens, but the second thing happening makes it harder for the first thing to happen, which makes it harder for the second, etc. Capitalism is one giant negative feedback loop that contradicts its own existence. It will eventually collapse; we need to make sure it collapses into socialism instead of fascism.