Die remkussing is oud.

Afrikaans usually writes compound nouns as a single word.
So:

• rem = brake
• kussing = cushion/pad

Together, remkussing is one compound noun meaning brake pad.

Is is the present-tense form of the verb wees meaning to be. It works like English is/am/are, but Afrikaans is simpler because the form is is used with all persons:

• ek is = I am
• jy is = you are
• hy/sy is = he/she is
• ons is = we are
• hulle is = they are

Because oud comes after is, so it is being used as a predicate adjective: is oud = is old.

In Afrikaans, adjectives often look different depending on where they appear. After is, you normally use the basic form, and here that form is oud.

Then you would usually say die ou remkussing for the old brake pad.

So compare:

• Die remkussing is oud. = The brake pad is old.
• die ou remkussing = the old brake pad

This is a very common pattern in Afrikaans: the adjective can look different before a noun than after is.

It would be:

Die remkussings is oud.

A few things to notice:

• remkussing becomes remkussings in the plural
• die stays die
• is also stays is

So Afrikaans does not change the article or the verb here the way English changes pad is to pads are.

You would say:

'n remkussing is oud.

Here 'n means a/an.

The sentence follows the normal Afrikaans main-clause pattern:

subject + verb + complement

So:

• Die remkussing = subject
• is = verb
• oud = complement/adjective

You can also think of it as the finite verb being in the second position, which is a very important Afrikaans pattern.

You would say:

Die remkussing is nie oud nie.

Afrikaans usually uses a double nie in negative sentences:

• first nie before the part being negated
• second nie near the end of the clause

That double-negative structure is one of the most important features of Afrikaans grammar.