Comparative and superlative degrees are used to compare the qualities or characteristics of different people, things, or actions in English grammar. Here are the rules for forming and using comparative and superlative degrees of adjectives and adverbs:

1. Comparative Degree of Adjectives:
To form the comparative degree of most adjectives, add -er to the end of the adjective. However, for longer adjectives, use more + adjective.

Example:
- Small (comparative: smaller)
- Beautiful (comparative: more beautiful)

2. Comparative Degree of Adverbs:
To form the comparative degree of adverbs, add -er to the end of the adverb. However, for adverbs ending in -y, change the -y to -i and add -er.

Example:
- Fast (comparative: faster)
- Happily (comparative: more happily)

3. Superlative Degree of Adjectives:
To form the superlative degree of most adjectives, add -est to the end of the adjective. However, for longer adjectives, use most + adjective.

Example:
- Small (superlative: smallest)
- Beautiful (superlative: most beautiful)

4. Superlative Degree of Adverbs:
To form the superlative degree of adverbs, add -est to the end of the adverb. However, for adverbs ending in -y, change the -y to -i and add -est.

Example:
- Fast (superlative: fastest)
- Happily (superlative: most happily)

5. Irregular Forms:
Some adjectives and adverbs have irregular comparative and superlative forms that do not follow the above rules. Here are some examples:

- Good (comparative: better, superlative: best)
- Bad (comparative: worse, superlative: worst)
- Well (adverb comparative: better, adverb superlative: best)
- Badly (adverb comparative: worse, adverb superlative: worst)

6. Comparison with "than":
When comparing two things, use "than" after the comparative degree.

Example:
- She is taller than her sister.

7. Comparison with "the":
When comparing more than two things, use "the" before the superlative degree.

Example:
- He is the tallest boy in the class.

Remember to always follow these rules to correctly form and use the comparative and superlative degrees of adjectives and adverbs in English grammar.