Bitcoin Payment Networks
Bitcoin can be used for day-to-day payments via the Lightning Network. This "Layer 2'' software is built on top of Bitcoin's base layer. Bitcoin's base layer is very secure, takes ten minutes for confirmation, and is somewhat expensive in terms of transaction fees. The Lightning Network is faster and cheaper for small transactions.
To transact on the Lightning Network users download a wallet app on a smartphone. One example is Phoenix Wallet.
One Bitcoin is divided into 100,000,000 satoshis or "sats." Costs on the Lightning Network are typically denominated in sats. To help train your brain for sats: If Bitcoin is trading for $30,000 USD then 10,000 sats buys a cup of coffee ($3) and 100,000 sats buys a bag of groceries ($30).
The following video gives a feel for sending and receiving Bitcoin. The video features both on-chain transactions (meaning through Bitcoin's secure, expensive base-layer) and Lightning transactions (faster and cheaper for everyday purchases).
Should Bitcoin become legal tender in a developed country, it is likely that corporate payment processors like Visa would be incentivized to build their own fast, cheap Bitcoin payment systems on top of Bitcoin's base layer.