Adding sound effects to iTUNES audio library


Can anyone share how to add your own sound effects to the iTunes library? Back in the olden days (2012) I was able to add by going to library/somewhere/somewhere/somewhere but I can't seem to figure out where there are now. I know how to find the effect online, download and drag into a movie, but would like to save clips I edit or find. I did find a folder called iLife sound effects with folders like People or Cars ... I tried saving as aiff then changing to caf and that doesn't work. Tried .wav, nope. Any hints? Thanks.