French builds comparisons the same way for almost everything, adjectives, adverbs, even quantities, with just three small words: plus (more), moins (less), and aussi (as).
1. Comparing adjectives and adverbs: plus/moins/aussi... que
| Il est plus grand que moi. | He is taller than me. |
| Elle est moins timide que sa sœur. | She is less shy than her sister. |
| Ce film est aussi intéressant que le livre. | This movie is as interesting as the book. |
2. Comparing quantities: plus de / moins de / autant de + noun
To compare amounts of a noun, use de (not an adjective) between the comparison word and the noun.
| J'ai plus de temps que toi. | I have more time than you. |
| Nous avons moins d'argent que vous. | We have less money than you. |
| Il mange autant de pain que moi. | He eats as much bread as me. |
3. Watch out: bon/bien have irregular comparatives
Not "plus bon": the adjective bon (good) becomes meilleur(e)(s) (better), and the adverb bien (well) becomes mieux (better). Ce gâteau est meilleur que l'autre. (This cake is better than the other.) Elle chante mieux que moi. (She sings better than me.)
4. The superlative: le/la/les plus... / le/la/les moins...
Add a definite article in front of the comparative. With an adjective, the article agrees with the noun; with an adverb, it's always invariable le.
| C'est le plus grand bâtiment de la ville. | It's the tallest building in the city. |
| C'est la plus belle plage. | It's the most beautiful beach. |
| Ce sont les meilleurs restaurants. | These are the best restaurants. |
| Il court le plus vite de l'équipe. | He runs the fastest on the team. (adverb, invariable le) |
5. Quick reference
| plus... que | more... than |
| moins... que | less... than |
| aussi... que | as... as |
| bon → meilleur | good → better (adjective) |
| bien → mieux | well → better (adverb) |
| le/la/les plus... | the most... |