1) Open the dmg you downloaded from rapidweaver.org. Double click the folder Stacks. Inside it you should see 6 stacks and a help file (the help file opens up this page).
1) Select the stacks you located.
2) Drag the stacks into your stacks folder. The folder is located in [Your username]/Library/Application Support/Rapidweaver/Stacks/
1) Create a stacks page in Rapidweaver. The stacks should be in the bottom of the library, they have blue icons with 1.3 on them.