You're a beginner; You're simply giving away pieces in your games.
There are certain principles that everyone has to learn to get better at chess. Opening principles, endgame principles, tactics, etc. It's just a matter of doing a bit of studying, and you'll see a quick improvement.
I have always been very good at chess, playing against a friend, or my dad, but I haven't won any games so far on this website. Is there any obvious reason, or am I just not used to it. Maybe I'm playing people who are way better than myself at chess, but I run into this problem even when I play against the computer... Any tips?