• there are no 'things', isolated from other 'things'; there exist only relations and processes, and these are all internally connected
• from this it follows that every relation is a contradiction, a unity of opposites
• these opposites are identical and different at the same time – they are distinct, in a way, but one cannot exist without the other, and they interpenetrate each other
• quantitative changes lead to qualitative leaps (progress is not linear), and
• change is constant, because contradiction is everywhere, in all ~~things~~ relations, processes.

In sum: DiaMat studies how the struggle of contradictory opposites drives change. If the 'relations'/'processes' bit throws you, try to think of something simple and analyse it in your head. Like a ball. It appears to be a thing, separate from other things.

But zoom in. The air pushes out while the rubber pushes in. Zoom in further, that rubber is imperfect, a mesh of tightly connected chemicals. There are tiny gaps, through which the air inside can slowly escape, meaning the air inside is connected – 'internally' related – to the air outside, even if the ball – seen as a 'thing' appears to be separate from that outside air.

A good way to understand DiaMat is to take some time to think about the above summary, then to read an example, then come back to the summary to see if you can identify the moves in the example. Then read another example and do the same thing again before delving into some of the theory.

If you want a good, concrete example, take a look at how Marx and Engels discuss the bourgeois and proletariat in the Communist Manifesto or read Marx, 'The Eighteenth Brumaire'. If you're up for a challenge, read the first 3 or 4 chapters of Capital to see how Marx applies DiaMat to explain the commodity.

For the theory, you might try:

• Lenin, 'Three Sources and Component Parts of Marxism',
• Engels, 'Socialism: Utopian and Scientific' (this includes extracts from his Anti-Duhring, and
• the Postface to the second German Edition of Capital, from and including the text 'The European Messenger of St. Petersburg in an article dealing exclusively with the method of Das Kapital (May number, 1872, pp. 427–436), finds my method of inquiry severely realistic, but my method of presentation, unfortunately, German-dialectical.…' (https://www.marxists.org/archive/marx/works/1867-c1/p3.htm)
• Mao, 'On Contradiction'.
• If you can find a copy, Bertell Ollman's Dance of the Dialectic is good (he used to have a copy on his website, but I've not been able to find it for a long time; the paperback is easy to find and there a likely other versions on the internet) – As are Maurice Cornforth's books on DiaMat and HiMat. These may be a better start. They're excellent.

Carlos L Garrido recently put together a collection of texts on DiaMat for Midwestern Marx. It looks good. Could be worth a read. There's also a good 'Marx, Engels, Lenin, Historical Materialism' collection from the Soviet Era. It's rare in physical form, I think, but there are PDFs.