If you have currency in your Jaxx wallet and wish to send it to someone else, you'll need to have their address of the same currency (ex. if you are planning on sending Dash to someone, make sure you are sending it to their Dash address).
If the sender has provided a QR code to scan, select the Camera button to scan it (mobile versions of Jaxx only):
Then specify the amount (in currency type or cash) and select Send.
If you are using Jaxx on a non-mobile device, you will not be able to scan a QR code. This means you will have to enter the address manually or through copying and pasting. Browser-extension versions of Jaxx scan web pages for valid bitcoin addresses and will list them in-app for your convenience.