Learn Finnish: Minä katsoin kattilan pohjaa. - I looked at the bottom of the pot.

The rule about dropping the first vowel of a diphthong applies to Verb Type 2 (like juoda becoming join). However, katsoa (to look) is a Type 1 verb. Its stem is katso-. Since it ends in a single -o rather than a diphthong, we just attach the past tense marker -i- and the personal ending -n to get katsoin.

Why is the word for "bottom" in the partitive case (pohjaa)?

The verb katsoa is a "partitive verb". This means the thing you are looking at must take the partitive case. While English uses the preposition "at" ("looked at the bottom"), Finnish expresses this relationship by simply using the partitive form pohjaa.

How does kattilan translate to "of the pot"?

In Finnish, possession is shown using the genitive case, which adds an -n to the end of the word. Instead of saying "the bottom of the pot" with a preposition, Finnish structures it as "the pot's bottom". Kattila (pot) becomes kattilan, and it is placed directly before the thing it owns (pohjaa).

Is the word Minä (I) strictly necessary here?