The simplified characters are often use in life. ( office, school, shop...). Many people like writing the simplified, because it is more easily than traditional.

Personally, I prefer Traditional Characters, but Simplified Characters seem easier for Western learners.

Traditional Characters: http://en.wikipedia.org/wiki/Traditional_Chinese_character Simplified Characters: http://en.wikipedia.org/wiki/%E7%AE%80%E4%BD%93%E5%AD%97

just some of the characters are different,they have the same pronunciation ,but different way of writing

Some Chinese thought some Chinese caracters are too complicated to write, and simplified them. People in China now use simplified Chinese as daily language, except in Hong kong and Taiwan. However, if you want to read the old books written by ancient Chinese writers, you'd better read the traditional Chinese caracters, otherwise, you may be misunderstand.