"The cooks are cooking soup."
Translation:Die Köche kochen Suppe.
If you're using a mobile app, I don't think it provides its own keyboard at all, but simply uses the system keyboard.
So you can install a German keyboard on your device, or you can try long-pressing the a o u s keys in order to get access to ä ö ü ß (as well as other versions of those letters such as à ó û š).
Ines, I believe you will be able to do umlauts if you ask a knowledgeable friend or search on the internet: “Make umlauts on . . . “ and add what kind of phone you have. Also, see Mizinamo above. “Long pressing“ means that you can hold the key down and a window will pop up with alternative characters. Just slide your finger over to one of those. Good luck! I think you'll be glad that you figured it out! :-)
What's the difference in plural endings between - e, - en, or innen?
der Koch is a male cook; its plural is die Köche.
In the dative case in the plural (where nouns almost always have an -n ending), it's den Köchen.
die Köchin is a female cook; its plural is die Köchinnen.
(In the dative case in the plural, the form doesn't change, since it already has an -n ending; it's simply den Köchinnen.)
Top tip, never rely on the drop down hints if you go ahead with the lesson, feeling unwell. In fact, consider 'buying' a day's pass. It is taking me forever, due to really daft mistakes. Worse, I failed to spot that Köchin was not cooks (it was given as the first option) , - because I feel awful. Weirdly 'ihrem' was like second nature. Back to the massacre.
Why isn't it not: Die köchen kochen suppe ?
You need the nominative case for the subject of a sentence -- so you need nominative Köche, not dative Köchen. "They" are cooking soup, not "Them" are cooking soup.
Also, the nouns Köche and Suppe have to be capitalised. (Unfortunately, Duolingo does not check that.)