两种方式:

1）：用Salesforce自带的在线开发模式

Setup --> App Setup --> Develop --> than you can select 'Pages', 'Apex Classes', 'Apex Triggers' ...... to select target file or create new file to do your development.

Another way is click 'Developer Console' this is the  special IDE of salesforce.

 

2）：在Eclipse中安装Salesforce的IDE插件

You can click this link to get the plugin step:  http://wiki.developerforce.com/page/Force.com_IDE_Installation_for_Eclipse_3.6