Almost every PC user uses email links on websites. Usually, such links have the following format:
When one clicks the link an email client will be opened automatically. The user will see the form for composing a new email that contains a recipient email address in the field "To". In other cases, different fields like the field "Subject" will contain the data too.
The same user-friendly way of interaction can be used with the crypto wallets too. BTC link has the following format:
bitcoin: 3AFaCnqriLNxj15kqtp5Pxn8puHfuqbX7W
If the user has a wallet application on their device and follows this link, the wallet application will open with the specified address. In this case, the user should make only one action to click a "Pay" button in order to proceed with the payment.
BTC URI supports not only the address but also other options, for example, a payment amount.
BTC URI has a special standard "BIP-0021" described here:
https://github.com/bitcoin/bips/blob/master/bip-0021.mediawiki