If you want to install a new texture for a default aircraft you have to make sure it's designed to "fit" a default texture. The description will say something like "replacement texture for default 747". This will typically contain only one folder called Texture.x with a few .bmp files in it.
If it's not intended as a replacement for a MS texture it will say something like "texture for John Doe's 747", in which case you will need John Doe's 747, which will have folders for panel, sound and texture. The addon textures for this plane will typically contain only folder called Texture.x with a few .bmp files in it but you CAN NOT freely swap MS textures with John Doe textures.
Most addon textures will also contain instructions for modifying your aircraft.cfg file so the sim can "see" the new texture. I'm not going to go into details now because you will see this in the instructions (readme) files.
I don't have Project Concorde so I can't help you with specific questions on it but if you practice with a few with English instructions and read these
http://www.simviation.com/acinstall.htm instructions you'll get the hang of it.