Depends if you downloaded the injectables--> .dtx files
Or the drag and drop ones --> .rez
For the .rez files, all you need to do is put it in your CA game folder (be sure to save a backup of the original file)
For the .dtx files, you need to open up RezInject, in the top bar, put the file you want to inject TO (Should be in the post of the creator). Then, click add, and put the file you want to inject. Press inject. After that, there should be two copies of the file, one with .rez and one with .rezNEW. Back up the one with .rez and take the "NEW" off the other one and you're done.