You need to choose a location for your instance. If you are using the default text store that comes with TiddlyWeb this will be a directory on the filesystem. This location is entirely up to you.

If you have installed tiddlywebwiki then you have a command called twinstance which is used to create a new instance. Select a directory where you want the instance to exist and then run the following command:

replacing "myInstanceDirectory" with the name of the directory to be created.