Go to the link below and scroll down until you find "Minecraft's unmodified files are a good place to start if you plan on making your own Add On. Download these zips of the resource packs and behavior packs and get creative!" Click on "resource packs" and "behavior packs". Then extract those zip folders with a program such as 7zip or winrar. Once you are done making your changes, use 7zip or winrar once again to turn those folders into zips. Then change the file extension to .mcpack and double click.
If you have any questions, feel free to PM me. Making mods is not a simple process, but with time you will become a master.
If by that you mean getting custom skins from the internet, there is currently no known way to do this on PS4 sadly. It is possible to do this on the Windows 10 and mobile versions of Bedrock however. Hope this helps!