Learn Finnish: Luen työpaikkailmoituksia netissä joka päivä. - I read job advertisements online every day.

The verb lukea (to read) describes an ongoing, incomplete action in this context. You are reading an unspecified number of ads without a specific endpoint, so the object must be in the partitive case. The -ia ending makes it plural.

How does the long compound word työpaikkailmoituksia break down?

It is made of three base words: työ (work), paikka (place), and ilmoitus (notice/advertisement). Työpaikka together means job or workplace. The final part is conjugated into the partitive plural.

In English we say 'on the internet', so why does Finnish use the inessive case netissä ('in' the internet)?

Finnish conceptualizes the internet as a virtual space or container that you are inside of, rather than a flat surface. Therefore, it takes the inessive ending -ssä instead of the adessive -llä.

Why is joka päivä (every day) in the basic nominative form instead of the essive case (joka päivänä)?

While days of the week and specific dates usually take the essive case to mean 'on' a day (like maanantaina), expressions starting with the pronoun joka (every) are an exception. The noun following joka always stays in the basic nominative form, so it is just joka päivä.