It'll get even easier as the book goes on, generally. Part one is especially dense because Marx wanted to make sure basically* everything in the book is deducible from the (extremely abstract) principles lain down in part 1. I can't remember offhand who in these threads pointed it out, but he even smuggles the labour-power / labour differentiation into part 1. Stuff becomes increasingly concrete from here on (especially in ch10 and ch15) as Marx shows how all the abstract principles of part 1 play out in real life.
*part 8 is something of an exception, but this is intentional on Marx's part (he's very explicit that primitive accumulation takes place outside the regular laws of capitalist production and so does not follow from the laws of part 1-7)
Page numbers from Fowkes penguin translation, emphasis is mine
It isn't a duality, it's a series of reflections (commodity-value -> exchange-value -> price). Commodity-value is the socially necessary labour in a commodity, exchange-value is it's reflection in another commodity and price is that exchange value in money. All three of them can differ from each other to some extent (particularly 'commodity-value/value', which can never be actually observed or measured except as seen in its reflection/likeness, exchange-value and the ). All three of these things' ability to diverge from each other is necessary for the capitalist system to function on its laws of averages. Exchange-value is the equivalent of a commodity's commodity-value in another commodity (e.g. the value of a shoe in ounces of gold). Price is a representation of the ratio in which a commodity can be exchanged for money.
Also very important to note (for feminism/ecological/ableism/etc critique) that Marx is laying out the standards of capitalist value, which doesn't necessarily represent the actual work/labour exerted on a given thing, e.g. doesn't represent the labour required to produce a forest cut down.