Hi there,
I can give you my thoughts on those terms, even though there's probably other guys with different ideas.
Glide and slip are the same. It has to do with how smoothly the razor slides over your face. Some soaps/creams just feel slicker, for whatever the reason.
Cushion and protection go together. Not enough cushion and the blade rests too closely on the face with no buffer. Might make your face feel a little bit raw, and not give you as much warning before something bad happens (less forgiving). However, too much cushion isn't good either, in that it keeps the blade from cutting as closely as it normally should. Bearing down a bit can help compensate for that, but why add another variable.
Personally, I use a fairly thin layer of lather (1/8 inch maybe?)......always the same depth. Now sometimes the razor will be louder on my face than usual. Also, I will feel the blade more than usual on my face. Third, the resulting shave will be a little closer than usual. All those things happen when using a lather with less cushion than I prefer. Same depth as the lathers I do like.....but they act differently. Too much cushion, and I gotta fight through the stuff. Heh, my shave is quieter too.
Skin care refers to the post shave part......how your face feels after the shave. Ideally, it will be in a better mood than before running a razor over it. Yeah, it will actually feel healthier........pretty weird. Less than perfect results can cause redness, tightness or dryness.
Something to think about is this lather thing is not always gonna work the same for every product.......not even close. Even after many years of using a brush it will still sometimes take me 3-4 times to figure out a new soap/cream. The thing is not to give up after 1-2 times, especially if the product gets good reviews. Sometimes it really does take some time to unlock the secret.
Anyway, maybe some of this will help.
Martin