NOTE: You must register on the forums to see downloadable attachments!
If the attachment is a script file (E.g., ActionName.cs):
Download the attachment and replace the existing file in your project.
If it's a new script, save it anywhere under Assets.
If the attachment is a unitypackage (E.g., NewActions.unitypackage):
Download the attachment and import it into your project.
This should put the contained actions in the proper directories.
NOTE: New versions of Playmaker will include any actions uploaded here.
If you get this error after downloading an action, or updating Playmaker:
Error CS0101: The namespace `HutongGames.PlayMaker.Actions' already contains a definition for XXXX
This means you have 2 actions with the same name. Type the name into the Project search field and you should quickly be able to find the duplicate files. Delete or move one of the files from your Assets folder to fix the error.