I learned to ride a bike late (when I was 30) so I'm clueless when it comes to bike maintenance. However, with youtube videos and helpful bike maintenance pages I've learned how to replace the tire/inner tube and some spokes. It's quite fun however I cannot figure out how to properly install the rear derailleur. I just bought this bike today (beater bike for $20) but the derailleur which was an old version did not stick and came out in the car. So I bought one recommended from the shop (Shimano RD-TX75) but those instructions are difficult to understand. By the way, I apologize in advance if this subject has been to death, but I cannot figure out what I'm doing wrong. I've checked all kinds of videos on how to install rear derailleurs, but they're all different than mine and it seems as if each derailleur has its own way of going on the bike. I've posted a pic below. By the way the bike is a Schwinn Sidewinder.
(i'm sorry the photo is upside down, i can't figure out how to undo that)