How does one pay with bitcoin?

How exactly does one pay with bitcoin? I've heard that it's a decentralized digital currency, but I'm not quite sure how the process works. Do you need a special app or wallet to hold your bitcoin? And once you have some, how do you actually send it to someone else as payment? I'm also curious about the security of using Bitcoin for payments - is it safe to use and are there any potential risks I should be aware of? Overall, I'm looking for a clear and concise explanation of the process of paying with bitcoin.