For anyone who has had a lot of trouble with learning the Korean alphabet on Duolingo
Turns out what Duolingo's teaching you is syllables, not the alphabet itself. I looked it up, and found this site: http://learn-hangul.com/#learn-hangul
It teaches you about the actual 'letters', which are then grouped into syllables. It made learning the syllables with Duolingo leaps and bounds easier!
UPDATE: It helped me so much that I had it memorized two days later!
You can also click on the little light bulb icon next to the start button for any particular skill set to get a brief lesson. Alphabet 1 has some info on syllable blocks, vowels, iotised vowels and diphthongs; Alphabet 2 on consonants; Alphabet 3 on the romanisation standard Duolingo uses and common transliteration to Korean; Basics 1 on nouns, articles, 'and' conjunctive, copula, plurals, omissions in Korean; and etc.
I'd highly recommend complimenting Duolingo with other sources. Language books, other websites, tutors if you can, eventually other media like movies, music, newspapers.