Luci-app-nft-qos traffic Priority

Hi, i have installed luci app nft qos. Now there is a option called traffic priority. now how can i enable it? for example: i want web browsing like facebook and youtube first priority, then downloading anything would be second priority, games like pubg, clash of clans third priority. How can i do that? how can i find the port number for fb, youtube, etc? how do i know which connection tcp or udp they use?