Does the usage of katakana in manga have any specific meaning? I don't read japanese, but I can distinguish katakana/hiragana./kanji

I've noticed that some mangas use a mixture of both. Does the usage of katakana in a primarily hiragana/kanji manga mean anything?
These two answer covers the topic very well:


  
  To describe (what feels like) Western origin words
  To describe onomatopoeia (e.g. sounds effects)
  To describe the fact that it is normally written in kanji, but that it is written without it because either the writer wants to write faster, has no access to the kanji form (as in the case where the writer is given the name in a romanized transcription or the writer just heard the name), forgot the kanji form, or does not want to bother to write in kanji for any other reason.
  To give visual and/or very slight semantic emphasis.  Almost like using bold or italics in English.
  


Most commonly katakana seen to be used for the #4. Much like how we can write in lowercase and UPPERCASE to give emphasis. Because it's sometimes difficult to feel the atmosphere when reading such emphasis is generally used in the words.

What most people don't immediate pick up is that much like reason #1, you can use katakana to emphasize foreign-sounding of a particular character speech. It's hard to transcribe a foreign accent (including some but not all verbal tics) in Japanese, but using katakana can get this idea across to the user. It's like if I were to talk to you normally, I would perhaps use a combination of hiragana and kanji, but if I were to talk to you and sound foreign, perhaps LIKE A ROBOT, I would used katakana. This so-called "technique" is used commonly in visual and written novels in Japan, not just for foreign sounding words, but also to emphasize the foreign-ness of a particular person's dialogue.



Hiragana can also be used in a similar fashion. Hiragana is typically the first reading/writing language a kid learns as they start reading in Japan. This is sometimes used to indicated the simpleness or naivety of a character, in general or at a specific moment. In the Yotsuba&amp; manga, the titular character Yotsuba's dialogue is written in hiragana without any kanji, emphasizing her simpler, childlike manner. She also has a slightly different sized and styled typeface to emphasize her intensity and energy as a kid. In addition much of these quirks like her pun-filled nuances are lost in subsequent localizations



Those are the most basic nuances to look for when reading manga. If you're interested in learning more about the language and manga I recommend checking out the book Japanese the Manga Way: An Illustrated Guide to Grammar and Structure by Wayne P. Lammers.