Instructions are given in the link.. but a point to remember, applications have to be on the internal memory before you create the link.
You can save space on internal memory.
As Samsung phones mount the memory card after boot.. everytime you boot you loose your widgets and sometimes you get mount errors.
How it works(in simple terms.. not exact)
It transfers and links applications on SD card to internal memory(/data)
its like creating a shortcut on desktop rather than saving the application on desktop...