To use the Newgrounds API in your Flash Builder project, you must add the NewgroundsAPI.swc to your Flash Builder library path:
Copy NewgroundsAPI.swc to your project folder.
Unzip NewgroundsAPI.zip, and copy the SWC file into the lib folder in your project directory.
Open the Library Path dialog.
Click the Project menu, and select Properties. Click on ActionScript Build Path, and select the Library Path tab.
Add NewgroundsAPI.swc to the library path.
Click the Add SWC button, and browse to the NewgroundsAPI.swc. NewgroundsAPI.swc should now appear in the Build Path Libraries list. Click the arrow to the left of NewgroundsAPI.swc, and ensure that the Link Type is set to Merged into code.
You are ready to go!
The Newgrounds API is now ready to use.