Are you writing SuiteScript 1.0 or 2.0? Either way, all of the API docs are located in Help. In 2.0, each module has its own dedicated page; in 1.0, the functions/objects are broken out into a page for each related group of functionality.
For 1.0, navigate in Help to SuiteCloud > SuiteScript 1.0 > SuiteScript 1.0 API
For 2.0, navigate in Help to SuiteCloud > SuiteScript 2.0 > SuiteScript 2.0 API > SuiteScript 2.0 Modules