There are some special QR code formats, that can be used to embed links, instructions to send a mail or SMS, WLAN credentials, etc in them.
To make it a bit easier I listed some of them here and added input fields for creating them quickly.
When you see ${VARIABLE_NAME} in the format, replace it with the corresponding value you want to use.
When you scan it with a phone, you will visit / be offered to visit the linked website
Format: ${URL}
When you scan the code you will be offered to join the network. No need to manually type the name or password.
Format: WIFI:T:WPA;S:${NETWORK_NAME};P:${PASSWORD};;