Choose Show Other Scripts from SpamSieve’s SpamSieve menu. Copy the files from the For Emailer Users folder into Emailer’s AppleScripts folder:

You may need to quit and re-launch Emailer in order for it to notice that you have installed the SpamSieve AppleScripts.
If you want SpamSieve to color messages that it thinks are spam, set up a mail action in Emailer that looks like this (using the Define Actions… button to set the “Run the AppleScript” action):

If, instead, you want SpamSieve to move suspected spam messages to a Spam folder (that it creates automatically), set up a mail action in Emailer that looks like this:

SpamSieve will now automatically color or move new spam messages that you receive, depending on which mail action you set up. If SpamSieve is not running when you receive new messages, it will launch automatically.