The Free Internet Chess Server, FICS, is one of the oldest and one of the largest internet chess servers. FICS has more than 300000 registered users. Here you can play chess over the internet for free, both serious games as well as just playing an occasional game.
What I also like about FICS is their Teaching Ladder, where you can submit your games to be annotated by stronger players. This is a perfect way to improve your Chess.
It’s free. Just try it. Their slogan is We do it for the game, not the money.
And to get the right experience I advice you to use a graphical interface like BabasChess instead of the Jin Applet.