Learn Finnish: Tyttöystävä odottaa meitä ulkona. - The girlfriend is waiting for us outside.

Meitä is the partitive form of the pronoun me (we). In Finnish, the verb odottaa (to wait for) always requires the person or thing you are waiting for to be in the partitive case. This is because waiting is an ongoing, continuous action.

Is there a separate word for "for" in "waiting for us"?

No, the concept of "for" is already built into how Finnish handles this action. While English uses the preposition "for" (wait for us), Finnish simply uses the verb odottaa followed by the partitive pronoun meitä. You never need an extra word for "for" with this verb.

Why does odottaa end with a double 'a'?

The verb stem here is odotta-. Because the subject is tyttöystävä (which acts as a "she"), we use the "hän" (he/she) verb form. In Finnish, you create this form by doubling the last vowel of the stem, which turns odotta- into odottaa.

How is the word tyttöystävä put together?

It is a compound word made of two parts: tyttö (girl) and ystävä (friend). Finnish uses many compound words, and they are often put together very literally just like this one.