Learn Finnish: Olin tehnyt pienen kuution puusta. - I had made a small cube out of wood.

Olin tehnyt is the pluperfect (past perfect) tense, which translates to 'had made.' You form it using the past tense of olla (olin) and the past participle of the main verb (tehnyt). Olen tehnyt is the perfect tense and would mean 'have made.'

Why do pienen and kuution end in -n rather than being in the partitive case?

They form the total object of the sentence. Because you completed the action and made one whole cube, Finnish uses the accusative case (which looks exactly like the genitive -n for singular nouns) instead of the partitive.

Why is the word for wood (puu) written as puusta?

The -sta ending is the elative case, meaning 'out of' or 'from.' In Finnish, when you specify the material something is made from, you use the elative case, mapping perfectly to the English phrase 'made out of wood.'

If the subject were 'we' instead of 'I', how would the verb change?

The sentence would start with olimme tehneet. In compound tenses, the helping verb olla changes to match the person (olimme), and the past participle changes to its plural form (tehneet) because the subject is plural.