Payments in Bitcoin
Payments are an important aspect of Bitcoin. Every transaction is a payment of some sort. Transactions are the only means through which information can be written onto the ledger. The process of block discovery is agreed upon through the acceptance of a coinbase transaction as a valid payment. A block is simply the process of having a collection of payments set down, collated and agreed upon as valid.
There are many different ways to request and make payments.
BIP-0021
BIP-0021has been one of the predominant means of making mobile payments in Bitcoin throughout it's history. Almost all QR codes used within Bitcoin are based on or an extention of BIP0021. It is an extension of [https://tools.ietf.org/html/rfc3986 the RFC standard for URIs (Universal Resource Identifiers).
BIP0070
[BIP0070] was a payment protocol for reaching out to receivers using an extension of BIP-0021 that added a URL. The URL directed the phone to reach out to a server and provide it the address at the front of the QR code. This server would instruct the device making the query which address to send money to.