The Summary section of the Cost explorer shows you the total cost of your subscriptions for the past 30 days.
Variations are subscriptions and resource groups that have seen their cost increase the most over the last 30 days. Clicking Variations will bring you to a detailed view of your variations per resource.
Potential savings shows you the amount you'd be able to potentially save if you were to apply ShareGate Overcast recommendations. Clicking Potential savings will take you to the Savings tab, where you can access the full list of recommendations.