Learn Swedish: Han köper fyrtio äpplen idag.

Swedish doesn't have a separate "-ing" form (continuous tense) like English does. Han köper translates to both "He buys" and "He is buying" depending on the context.

How does the plural form äpplen work?

The singular word for apple is ett äpple. Because it is an ett word that ends in a vowel, you just add an -n to the end to make it plural: äpplen (apples).

Is fyrtio actually pronounced the way it's spelled?

Not usually! While it is spelled fyrtio, in spoken Swedish it almost always sounds like "förti". The -tio at the end of numbers like 30, 40, and 50 is typically shortened to just sound like "ti" in conversation.

Why is idag written as one word instead of two?

You will actually see it written both ways: idag and i dag. Both are completely correct in Swedish, though writing it as one word is very common for everyday time expressions.