Some file formats (e.g. html, png) will be viewable in your browser, and will appear as clickable links below that will open the file once you've fully extracted your archive. Other file types can be opened by their appropriate applications by navigating through the archive's directory. You can click on any folders that may be present to see their contents.
Data that are still in the process of being deleted are not included in your archive.
Learn more about your deleted data.
Below are all the possible formats you could have received in your archive:
Activities
Workouts and automatically tracked activities, like running or cycling.
Daily activity metrics
Daily totals for each activity metric, like steps and distance.
All Data
All your data from Google Fit, grouped by source.
All sessions
All the sessions recorded in Journal, including activities and sleep.