Drag the SpamSieve icon onto the Applications folder. Double-click the Applications folder to open it. Double-click the SpamSieve icon to launch it. Eject the white SpamSieve-2.9.1 icon.
It is important that SpamSieve be installed directly in the Applications folder (not in another folder, or in a subfolder), because otherwise your mail program might not be able to find it.

Next, you must follow the instructions in the Using SpamSieve section in order to set up your mail program to use SpamSieve.