Need help completing add-on installations

I'm a newbie to all of this and need easy to understand help. When I download some planes like the Concorde the gauges are missing. I had the right gauges for it, but couldn't understand how to install them. Now I forgot where I got the gauges and I don't have them anymore. Also, I downloaded the Lockheed C-141 B Starlifter which came with gauge, sound, and effects folders. I tried following the installation instructions, but it didn't work. I need simple, good advice on how to complete my planes. Thanks. 
