Discord.py - Finding information about the sender

I am making a simple discord bot and am trying to find out the channel and sender of a message, so for example when someome types d!salute blah it will reply with "<SENDER> saluted blah!", accompanied by an image. I currently only really know how to use client.say, which finds the channel for me. What I want to know is how to retrieve both the channel a message is sent from and also the sender of the command. Thanks