Learn Polish: Ten człowiek umarł dwa dni temu.

dni is the highly irregular plural of dzień. It drops the -e- and changes the starting consonants. With numbers like dwa (two), trzy (three), and cztery (four), we use this standard plural form. So 'two days' is dwa dni.

This lesson is about irregular plurals. What is the plural of człowiek if we wanted to say 'These people died'?

The noun człowiek (human/man) is perfectly relevant here because its plural is a completely different word: ludzie (people). To say 'These people died', you would change the whole phrase to Ci ludzie umarli.

How does the word temu (ago) work in a sentence?

Just like in English, the word temu always comes immediately after the amount of time it describes. The Polish phrase dwa dni temu follows the exact same word order as 'two days ago'.

Is umarł a regular past tense verb?

It is slightly irregular. It comes from the infinitive umrzeć (to die). For a masculine singular subject like człowiek, the stem shifts in the past tense to give us umarł (he died).