Twitch is a popular live stream platform, on it users can post emotes which have names. One of the oldest and most popular emotes is pogchamp, it used to be the face of a streamer who made the expression after winning a game of pog but he got banned for some controversial statements (typical right wing covid denial, jan6th apologia) and the emote was replaced with a lizard making a similar face. This has slowly bled into the mainstream just as the word pog or poggers.
The facial expression sums up it’s meaning, but it’s basically one of shocked happiness, you would use it if a streamer does something rare/lucky/skillful. Luke sky-walker turning off his targeting computer but still destroying the deathstar is poggers. Getting an A on a multiple choice test despite guessing every answer is poggers.