Learn Finnish: Minä en muista lääkärin numeroa. - I do not remember the doctor's number.

To show possession (like the English 's), Finnish adds the ending -n to the end of the word. Here, the base word is lääkäri (doctor), so adding -n makes it lääkärin (the doctor's). This is called the genitive case.

Does the possessive word always come before the thing it owns, like in lääkärin numeroa?

Yes! Just like in English when we say the doctor's number, the Finnish possessive word (lääkärin) comes directly before the noun it owns (numeroa).

Why does the word for number have an -a at the end (numeroa)?

Because this is a negative sentence (en muista). In Finnish, when you have a negative action, the object of the sentence (the thing you don't remember) must be in the partitive case. So the base word numero becomes numeroa.

Why is the verb muista missing its personal ending here?

When you make a sentence negative, the negative word takes the personal ending (here, en for I do not). The main verb that follows just uses its basic stem without any personal endings. So it is Minä en muista, not Minä en muistan.