The pillar of Japanese writing
Kanji are written characters of Chinese origin that make learning Japanese complicated, but so much more methodical.
The use of kanji
Before the import of kanji to Japan in the 5th century, the Japanese had no writing system. Once introduced, they adapted the pronunciation of the Chinese ideograms to the Japanese language, and today almost all Japanese words can be written in kanji. There are more than 10,000 characters listed as kanji, which can be discouraging when thinking about learning Japanese. Yet in reality only around 2,000 kanji are used in everyday life.
Kanji are accompanied by two syllabaries, called hiragana and katakana (or kana), which are themselves derived from kanji and form two tables of 46 signs representing all the sounds present in the Japanese language. You can write Japanese using just kana, but homonyms are so numerous in Japanese that it would be very difficult to comprehend. So the use of kanji is justified!
A complex system
Learning kanji requires great dedication. Each ideogram has a meaning and a particular stroke order (way of writing), with several meanings and also several different readings. There are two types of reading, on-yomi and kun-yomi, respectively the Sino-Japanese reading and the Japanese reading. Thus the Japanese have adapted the Chinese writing system to their language by adding their own phonetics.
Although it seems difficult to remember all these characters, some methods can help to make learning the meanings of kanji a little easier. We can break down the most complicated kanji ideograms (some have more than twenty strokes!), and find radicals (key symbols) that appear in many kanji. There are about 200 radicals, and they help a lot in understanding, especially when they "look like" the idea they are trying to convey ( for example 木: tree, 林: wood, 森: forest).
Japanese and kanji
In elementary school Japanese children learn more than a thousand kanji, and this is just the beginning. However, the Japanese will still come across words they can't read or write throughout their lives. Ones that aren't used every day are quickly forgotten, especially nowadays when we don't write by hand as often. It's not uncommon to see Japanese television programs in which guests (often graduates of prestigious universities) must find the readings, detect errors, or guess the meaning of unusual kanji they are presented with.
Lastly, surnames and forenames remain the most difficult aspect of kanji to master. Even though there are many common names, you must be wary because some people who have the same combination of kanji in their names won't pronounce it the same way, and the Japanese are increasingly likely to choose more unusual readings of kanji for the names of their children. This makes the task even more difficult if, for example, a Japanese colleague gives you his business card. This doesn't mean that you have worry, because the reading can be clarified in person.