The idea behind the skipping is that you when you combine multiple tokens, you allow it to skip some and consider some others further ahead. 
Eg. if you have the tokens ["a", "b", "c", "d",] and you specify n_grams = 2 and skips = 2, you will get :
["a", "ab", "ac" (skipped 1), "ad" (skipped 2), "b", "bc", "bd" (skipped 1), "c", "cd", "d"].