External speakers must be connected to the sound port on the computer. You cannot install internal speakers. Camera has to be external too. Find a camera that works with your operating system. See you manual for more info-- https://www.dell.com/support/home/us/en/04/product-support/product/optiplex-755/manuals

Thank you

Did see mini speakers online don't know if they will work 

Also saw a USB camera online also manuals don't really show this