It depends on the character.
This is the character for forest. It is easy to picture this character as a group of trees.
[SIZE=+4]森[/SIZE]
The Chinese pronounce this as "shin". The Japanese pronounce it as "mori". This character can be pronounced "shin" in Japan, but if it is pronounced "shin", then that character is used to mean something other than a forest (example, someone's name).
Clear as mud?
Toexpand silghtly, within the Japanese written language, almost every character has at least two pronuncations, on'yomi and kun'yomi.
On'yomi are based on the way the Japanese believed the Chinese originally pronounced the characters themselves (to get even more confusing, as the particular characters could be taken from different parts of China over different periods of time, on'yomi could be classed as go-on, kan-on, to-on, or kan'yo-on depending on the region and time, or even a variety of these, giving multiple on'yomi pronunciations!). These are, as said, the way the Japanese thought the Chinese pronounced the words/concepts that the characters represented.
Kun'yomi is the native pronunciation of the concepts behind the characters. This is the original sound/word that the Japanese used to convey a particular idea or concept, the written version then borrowed, or taken from the Chinese written language.
This then gives us the multiple pronunciations, and while one or another may be used to show a slight difference, it is not necessarily that way either. After all, the character itself doesn't change, nor does the actual meaning, although a single character can be used to get across a multitude of concepts. I sometimes think that a primary reason for having the multiple pronunciations is simply to allow the language to clarify itself, as Japanese is only made up of two dozen or so syllables, so the combinations can be a bit limited.
Think of a syllable like "do". This can mean a number of things, in martial arts, the two most common are "way/path" and "trunk (of the body)", both of which are obviously quite different concepts, and use different characters accordingly. So to clarify, you can talk about "do", and clarify that you are refering to "michi" (path/street/way) or "mi" (body/trunk). Still clear as mud?
Oh, and while I'm here, Kuk Sa Nim, a small thing. The word you were looking for is "jutsu", rather than "jitsu", as they are completely different words. "Jutsu" means "art, practical skill", whereas "jitsu" means "truth". It's similar to writing "pen" when you are asking for a "pan" to cook in.