Learn Polish: Ona wszystko doskonale zorganizowała na dzisiaj. - She organized everything perfectly for today.

It is the direct object of the verb zorganizowała (organized), which means it requires the Accusative case. The helpful thing to remember for this lesson is that for the word wszystko (everything), the Accusative form looks exactly the same as the Nominative form.

Could I put wszystko after the verb and say Ona zorganizowała wszystko...?

Yes, you can. Polish word order is very flexible. However, short pronouns like wszystko or to frequently jump in front of the verb to make the sentence flow more naturally. Both versions are correct, but the word order in this sentence is very common.

Why do we use na dzisiaj instead of dla dzisiaj to mean 'for today'?

When you are scheduling an event, setting a deadline, or preparing something for a specific time, you use the preposition na. The word dla is generally used when doing something for a person's benefit, not for a point in time.

How does the adverb doskonale (perfectly) get its ending?

It comes from the adjective doskonały (perfect). In Polish, adjectives ending in -ły usually change to -le to become adverbs. The hard ł sound softens into an l, giving us doskonale.