Mapping topics allows you to determine which version of a topic of the same name appears on each of your stores. For example, you can use this feature to make multiple versions of the 'hometopintro' topic, to have different landing pages on each of your stores.
1 - First, if you want Topics to vary from store to store, you need to set the AllowTopicFiltering GlobalConfigs to true.
2 - Next, go to Content -> Topics. By default, all of the topics that are required for a store to function 'out of the box' are already created, and mapped to the default store:
3 - To add an additional copy of an existing topic, click the Add New button at the top of the page, and fill in the required fields. The name, title, etc may be the same as the default store's copy of this topic if desired.
4 - At the bottom of the form, change the "Map to Stores:" dropdown to the store you want to assign this topic to. If this topic will be applied across all stores, choose the 'Default for all Stores' option. Once you've made your selection, click the 'Add Topic' button to save the changes.
5 - Restart the site (to refresh the front-end cache), and you should see different versions of the topic on each store: