Hi, just started with Japanese and learned the Hiragana pretty quickly. But why is Katana introduced right after them at level 5? It messes up all the work I have done Hiragana. I was expecting for Kanji and now I have to stop and learn Katakana. I have understood that it is used for writing foreign names, I have no interest in learning foreign names in japanese ,I want to learn japanese names. I could understand that Katakana would be teached later, much later. Now it is just a sudden pain in the ass, just as I had the feeling that everything is going fine.
They sprinkle katakana throughout the course, it is not as concentrated as the hiragana lessons. As for the usage, katakana is used for foreign words, names and places, some Japanese names, a whole bunch of super common loanwords and abbreviations from the last century, often certain native Japanese words, animals, plants, or sometimes just for emphasis and style choices. Basically every piece of actual text you read. It is absolutely necessary.
It is not only about names! Many everyday words are written in Katakana, e.g. table - テーブル or airport - エアポート.
I think that Duolingo should teach Hiragana in the same time with Katakana. It is not motivating, when you are happy that you learnt the alphabet and then, you have to learn another one, again. Like you, I learnt Hiragana with ease and struggled more with Katakana.
I recommend the app "Human Japanese" to learn Katakana. It worked well for me, and I have almost all of the Katakana characters memorized after just a few days. The one problem is that the free version doesn't go over all of them, so you will have to buy the full version if you want to use the app for every single one. Still, the free version goes through most of them, and can be used for hiragana practice as well. It also teaches some new Japanese words that are very useful. You should definitely check it out.
Just like the other comments said, it is a good idea to learn katakana because food names are also in katakana. So if you read a Japanese blog, or go to Japan and read a menu, or something like that, then you can read it.
Don't be discouraged! Learning 3 different alphabets in a single language throws a lot of people off, including me. Unfortunately, learning Katakana isn't really optional; you have to pick it up at some point, like English punctuation. Sure you could get away with writing a few sentences without commas and fancy semicolons, but it's impossible to avoid them when you read English texts. The earlier you learn it, the easier it will be to handle in the future.
The same applies to Japanese! Forgoing one aspect (or alphabet, in this case) of a language isn't the brightest idea since it limits your ability to read or express yourself. The best thing you can do right now is to review the Katakana characters so that they're rock solid in your memory before the lessons throw more at you. The more you review, the more confident you'll be, which is a huge step in the right direction when tackling a language! I used Tinycards for memory, which has helped me a ton, but any other set of online or physical flashcards should work fine.
PS: You'll get Duolingo XP from doing these, so they'll help you level up as well!
I suggest you use the app memrise. And as others have mentioned, katakana is not only for foreign names, but for all sorts of things. My point of view - I slacked with katakana in the beginning, with almost the same reasoning as you. Now it's evident, that I lack reading proficiency with katakana. Which is a mistake and I had to review katakana and put additional effort to read it quickly and accurately. Hiragana is in intermediate japanese used basicaly only for particles, everything else is written with kanji and katakana. And there are lot of everyday words written with katakana, many food items, movie names, foreign cities/countries/people names, appliances (レンジ、オーブン、テレビ、アイコン。。。）etc,etc, don't slack on katakana.
Learn it and love it, the katakana is easier to look at in my opinion. For me the hard part is that the Japanese pronounce the foreign (mostly Enlgish) words quite a bit differently than the regular English pronunciation so you can't just say the English word with its normal pronunciation. They probably won't get it. You need to learn to say these words their way. And guessing the right way is not easy either. Coffee is Ko- hi- コーヒー, and there are two ways to say Cup コップ,カップ, ハンバーガ, ハンバーグ hmm? Have fun!!