just as the title,i need to realize a function,how to find the API i needed,there is so many APIs……
In the Unity editor, click on the help tab. Go down until you see scripting reference. That’s where you will find it.
my question actually is,for example ,i need the object move with cursor or finger(On os or andriod),how to find the API i need in the scripting reference,there must be some way except check one by one ?
http://docs.unity3d.com/Documentation/ScriptReference/20_class_hierarchy.html
There is a search field in the top left corner. Other than that, you won’t have much choice to either google or search through the Script refence above. After a few weeks you will know most of the APIs and won’t have to look to often into the docs or you will know where to look. It’s a part of the job. When you begin programming you spend almost more time reading the API/Docs or looking for patterns/algorithms than programming itself.
No magic do it instantly button. That’s why people hire programmers to do the programming and don’t do it themselves 
On top of that, Unity3D API is pretty small, so you shouldn’t complain about having to look/read it. It just has a handful of classes. .NET/Mono Api is much bigger with way over 25.000 Types. No programmer would ever be able to know all of the 25.000+ Types in .NET. You just learn a handful of useful ones and everything else you look in the Documentation
thank you ,i got it