Are you not familiar with how the Japanese writing system works? Japanese kanji aren't just random ideographs, they're used to represent words that have readings (pronunciations). For example, the Japanese word for novel is 小説, pronounced as しょうせつ or "shousetsu". To type those kanji, they would type out "shousetsu" (on a PC, with that alphabetic spelling or with a keyboard that maps to the kana characters しょうせつ; on a smartphone, usually with a
flick input), and from there a list of kanji would pop up and you'd choose 小説.
You can find more information here:
Japanese input method - Wikipedia
I'll let someone else answer the question about Chinese, since I don't speak/read Chinese. Or maybe you can learn something from this wikipedia article:
Chinese input methods for computers - Wikipedia
P.S. To clarify, the above sites are specifically used to look up unfamiliar kanji characters whose readings you may not know. They're
not a standard way for Japanese speakers to input text.