MINECRAFT error. PLEASE HELP!!!!

I am currently trying to get some mods for minecraft. I have already tried to do the 7-zip copy and paste method but for some reason I'm doing something wrong. Furthermore every time I try to open up the minecraft .jar file it gives me a "Failed to load mainclass attribute...". Can anyone suggest a solution? Does the error even have anything to do with modding?

Help is appreciated!!

The mods need to be updated to the current minecraft version in order to work. Also, most mods that I have seen come with install instructions. Some that i use even have its own installer. I had to follow the instructions to the letter or else I had errors with my minecraft as well.