Learn Finnish: Aamulla syön puuroa ja juon kahvia. - In the morning I eat porridge and drink coffee.

In English you say "in the morning", but Finnish uses the adessive case (-lla / -llä) for general or recurring times of the day. You can contrast this with the essive case (-na / -nä), which is used when talking about a specific single morning, such as tänä aamuna (this morning).

Why are the words for porridge and coffee in the partitive case (puuroa, kahvia)?

Because they are uncountable mass nouns. If you were eating a whole, single countable item, like an apple, you would use the accusative object case (syön omenan). But when you consume an unspecified amount of a mass food or drink, Finnish requires the partitive case.

Why is the word for "I" (minä) missing from this sentence?

In standard written Finnish, first and second-person pronouns are usually dropped because the verb endings (-n in syön and juon) already indicate who is acting. However, in casual spoken Finnish, you will often hear people keep the pronoun and say something like mä syön.

Could I put aamulla at the end of the sentence instead?

Yes, Syön puuroa ja juon kahvia aamulla is grammatically correct. Moving aamulla to the front of the sentence just sets the scene first and slightly shifts the emphasis, much like the difference between "In the morning, I eat porridge" and "I eat porridge in the morning."