To compare two things in German, you form the comparative by adding -er to the adjective. Many one-syllable adjectives with the vowels a, o, or u also take an umlaut in the comparative. For example, groß becomes größer, as in Berlin ist größer als München (Berlin is bigger than Munich). The superlative is formed with am plus the adjective stem plus -sten, so groß becomes am größten, and you can say Berlin ist am größten (Berlin is the biggest). Adjectives ending in -el, -er, or -en often drop the -e- in the comparative, as seen with teuer becoming teurer (not teuerer) and the corresponding superlative am teuersten.
Some adjectives are irregular and follow their own patterns. The word gut (good) has the comparative besser and the superlative am besten. So you might say Das Essen hier ist besser (The food here is better) and Dieses Restaurant ist am besten (This restaurant is the best). The word viel (much or many) is also irregular, with comparative mehr and superlative am meisten. For example, Er arbeitet mehr als ich means He works more than I do, and Sie arbeitet am meisten means She works the most. These irregular forms must simply be memorized because they do not follow the regular -er pattern.
Comparisons are typically constructed with als (than) when comparing two things, as in Der Zug ist schneller als das Auto (The train is faster than the car). To express that something is excessive in a particular quality, you can use zu plus the adjective, as in Das ist mir zu teuer (That is too expensive for me). Comparisons are essential for daily life in German, whether you are comparing cities, food, prices, or the speed of different modes of transport.