How do I pay with Polkadot?

Could you please explain to me the process of making payments using Polkadot? I'm interested in understanding the steps involved, including any necessary prerequisites or accounts I may need to set up. Also, could you clarify if there are any specific fees or charges associated with making payments through Polkadot? Additionally, I'm curious about the security measures employed by Polkadot to ensure the safety of transactions. Would you mind elaborating on these points? Thank you for your assistance.