Hiragana and Katakana can be considered to be the basic building blocks of the Japanese language. While Kanji (Borrowed Chinese characters) does have a huge role in Japanese writing, all of the words that any Kanji character can represent can be shown using Hiragana or Katakana.
What’s the difference?
Hiragana tends to be used for words that are native to Japan (although there are exceptions). Hiragana also tends to be used for words which do not have a kanji character associated with the word, or if the kanji is rare enough the writer may opt to use the hiragana instead.
Katakana is typically used for loan words. Usually it is not used for Chinese loan words (ie. We can use Kanji instead), although sometimes they can be used for that purpose as well. Katakana is also used for onomatopoeia in Manga as well.
How Fast can I learn the Kana?
This largely depends on how much time you have to practice. There are 46 basic hiragana characters, and another 46 for katakana. The good news is you have some similarities with the characters so you aren’t learning 92 characters that are completely different, there is some overlap.
Everyone will vary. Some people can learn the all of the kana and modifiers within a week, others a month or more. It really depends how much time you have to dedicate to the task. Practice is very important as well. A general rule that my university had followed was 1 week for hiragana and 1 week for katakana. In the span of two weeks we were expected to have learned all the Kana including their modifiers (eg. が、ぎ).
So a good time frame to have is learning the kana within 2 weeks. This should be doable with 1 hour of study per day
(This is greatly exaggerating the time needed, we only did 4 hours of study per week at my university, meaning within 8 hours we were expected to learn all of the 92 sounds that the hiragana and katakana would produce).
I can read it, but I can’t write! What should I do?!
Relax, this is something that is inevitable with learning Japanese, and any other language for that matter. Chances are that before you fully learn how to write out the kana, you will be able to recognize them. This is a GOOD thing. This simply means that you are able to remember the kana.
Repetition is simply the best way to remember how to write the kana. At my university we did it the old-fashioned way, pencil and paper. You might be wondering why I’m not recommending apps like Obenkyo or Anki now, that’s because these apps are wonderful for getting you introduced into the kana and helps you to remember them, but the best way (at least in my opinion) to learn how to write them is simply to keep writing them out. Spending 20-30 minutes a day writing out the characters and testing yourself is a great way of practicing. Before you know it you’ll be able to write all the kana!
The sooner you do this the better though, since the kana are seen so frequently in Japanese that as you further your studies, it will become difficult to forget the basic kana.