I got those messages, too, @Catherine1535 , and I agree that they are nothing if not vague.
To see what you have in place already, on a laptop, go in as if to edit your listing. Choose the Pricing tab. Scroll down to Standard Fees and Charges and look at "Security deposit". If there is nothing there, you are correct and you merely received an automated message. If you wish to change what is there, just hit the Edit button and follow the prompts.
To find your pre-booking message, go to the Booking Settings tab. Click Edit beside Guest Requirements. Scroll down until you find Guest Trip Information. Hit the Edit button if you want to change it - but the wording of that message from Airbnb does make it sound as if this particular feature will be gone soon.
Did that help?