Arena was the standalone version of the CQC game within Elite Dangerous. It was for a while sold separately to the main game (and one weekend was available for free). It's now only available as part of Elite Dangerous but if you bought the standalone version it continues to work.
It's a light spaceship skirmish game (player-vs-player only) with fun combat - once you get past the steep learning curve - but because it's lacking some of the framework it needs (lobby chat/match browser) it has a low (slowly increasing) player base and it can be difficult to get a match at times. Best times are probably European/US evenings and weekends, with Deathmatch being the most populated mode.
A lot of the regular players can be found on the "unofficial lobby chat" Discord server and will be happy to help you find a match / point you to matches in progress / give you tips to help you through the learning curve.
https://discord.me/elitedangerouscqc
