I just wanted to know if there is anyway to download mods for star wars empire at war which I bought from the app store on my macbook air. If there is anyway to download mods can someone help me?

I don't know either of those platforms, but if a mod is compatible with your version/os then you should just download from a site like moddb and follow the instructions in the mod to install it - more or less every mod is different to install, so without further information can't see how we would help.

I get that But I go to those websites and is give instructions for downloading the mods on actual computers and I just do not know which mods i can run on my macbook because some mods are not supported on my laptop and I do not know where to put the mods to make them work.

Again, it's very hard to say with any certainty without information. What mod specifically? If the game runs on your machine, then it's possible that mods will. For instance if you download a texture pack for game a and game a runs on your machine, then you just open the compressed file and copy the files over to the install directory. If it's an installer, then likely not, although you could just run the windows version through wine or something like that.
As for how to use the mods, this is different for every mod, there is no one set of directions fits all.

I have gone to those websites but I do not know which ones are supported on mac and when I find one that is supported I do not know where to put the files.