After you imported the script it will be enabled (you can check in Plus > Preferences > General > Scripts or throught the scripting icon > Scripts Preferences)
To make it work as you want you'll need to edit the .INI to apply rules (what it is to do and when etc). You can find this file aswell as a readme.txt in C:\Program Files\Messenger Plus! Live\Scripts\Auto Answer
Edit: this is not the most userfriendliest/easiest script to use. For a simpler one (with GUI) you may want to look at Answering Machine Plus
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