I don't recommend giving all permissions to everyone on every file since that's not secure at all and puts your website at risk for being hacked and destroyed.
But if you need to chmod all files you can do so by following the below instructions.
Once again giving 777 permissions in public directory is not advised..
But if you need or want for some reason here's how to do so.
chmod -R 777 /home/admin/domains/domain_name/public_html/folder/
Also if you want to learn more about chmod you can
type man chmod in the terminal
Once again giving 777 permissions to files in public directory is not a good idea and if you're just testing something out you need to reset the permissions before making the website go live and available to the public otherwise you risk having your website hacked or destroyed.