Learn Finnish: Uusi sairaanhoitaja on jo ammattilainen. - The new nurse is already a professional.

The translative case is used when someone or something changes into a new state or role. Because this sentence uses the verb olla (to be), it describes a current, stable state rather than a change, so we use the basic nominative case. If the sentence said the nurse became a professional, you would use the translative: tuli ammattilaiseksi.

How is the compound word sairaanhoitaja put together?

It combines sairaan, the genitive form of sairas (sick), with hoitaja (carer or nurse). Literally, it translates to a carer of the sick.

What is the purpose of the -lainen ending on ammattilainen?

The suffix -lainen is added to nouns to describe a person associated with that thing. Here, it attaches to ammatti (profession) to create the word for a professional. You might already know this suffix from nationalities like suomalainen (Finn).