Learn Finnish: Aviomies ymmärtää meitä hyvin. - The husband understands us well.

Meitä is the partitive form of me (we). In Finnish, verbs that express thoughts, feelings, or continuous actions take an object in the partitive case. Because ymmärtää (to understand) is an abstract, ongoing mental action, it requires the partitive pronoun meitä.

Is aviomies a compound word?

Yes, it is! Mies means 'man', and avio refers to marriage. So aviomies literally means 'marriage man', which is the specific word for husband. You will also see this in words like aviovaimo (wife).

Can I just say mies instead of aviomies?

Yes! In everyday spoken Finnish, people very often just use mies (man) to mean husband, especially when it is clear from context. Aviomies is simply the more formal and specific word.

Why does ymmärtää end with a double ä in this sentence?

This is the 'he/she/it' form of the verb. In Finnish, to create the third-person singular form for most verbs, you take the verb stem and double its last vowel. The stem here is ymmärtä-, so doubling the final ä gives us ymmärtää (he understands).