How do you calculate 12% interest on a bank?

Excuse me, could you please clarify how one would go about calculating a 12% interest rate on a bank account? I'm curious to understand the process, as I'm looking to invest my savings and want to ensure I'm getting the best return possible. Is there a specific formula or method that banks typically use to determine the interest earned on a given amount of money over time? Any insights you could provide would be greatly appreciated.