This grammar/usage lesson is on comparisons of adjectives and adverbs and also on Double Negatives.

The comparison section includes how to make the comparative and superlative forms for shorter words and longer words, and it also contains the irregular comparisons of good, better, best, bad, worse, and worst, and the difference between good and well. 

The Double Negative section contains an explanation of what double negatives are, how to avoid them, and some humorous examples.