Parts of this chapter are easier to understand if you imagine yourself in a commodity-money society. For example –

"a relation between two commodities such that the one commodity, whose own value is supposed to be expressed, counts directly only as a use-value, whereas the other commodity, in which that value is to be expressed, counts directly only as an exchange-value."

Imagine you live in a commodity-money society where everything is bought in beans. Presumably it's called Beanland or Beantopia. If I want to buy a television, I am only interested in its use-value; I hand over a certain amount of beans for the tv, and I'm only interested in beans for their exchange-value, not their usefulness as beans in generating farts.

"Since a commodity cannot be related to itself as equivalent, and therefore cannot make its own physical shape into the expression of its own value, it must be related to another commodity as equivalent, and therefore must make the physical shape of another commodity into its own value-form."

Beans are the physical form value takes. A television has its own value. Say its value is 5kg of beans. Then the beans are the "physical shape" that are the "expression" of the value of the tv.

'Relative form' and 'equivalent form'

The discussion of 'relative form' and 'equivalent form' is just saying that when you say 'x units of commodity A is as valuable as z units of commodity B', you conceptualise commodity A in a certain way (which he calls the relative form) and commodity B in the equivalent form. In Beantopia, beans are usually in the equivalent form. The equivalent form is when we use a commodity as a measuring-stick.