https://fediversity.site/help/guide/en/Location_ServicesTo activate, you either need to include a latitude+longitude location in your settings or in a post you are creating. The referenced documentation explains the different settings and services and how to use them.
The TL;DR instructions:
Create a post. Click the globe icon in the post editor and 'Set your location'. Enter a period to use your current device location. Then click the globe again and select Checkin or Checkout to turn the current post into the associated activity.
Other fediverse software may or may not display a map and some may not show these activities at all.