Before creating a new PPS Planning application, it is best to set up your shared directories first. These will store your PPS Excel forms and reports, and the paths will be required when you set up the application in the Planning Administration console. Also, you should just copy and past the machine path into the appropriate boxes during setup.
You will need to create a shared data store to fill in when creating an application, so it's a good idea to start with this. Otherwise, you will need to create the stores during set up.