It doesn´t matter how long the adjective is, the comparative is formed by adding „-er“ to the basic form. A similar pattern applies to the superlative. The adjective comes after the noun and you simply add „-sten“ and use the word „am“ in front of the superlative.
For the most adjectives you simply add „-er“ in the comparative form and most of the monosyllabic adjectives with stem vowels a, o or u also add „-er“ but the vowels change to an umlaut (ä, ö or ü). Note: there are a few exceptions.
For the most adjectives the superlative is formed by adding „-sten“ to the adjective and the word „am“ is in front of the adjective. Note that most monosyllabic adjectives with stem vowels a, o, u add „sten“ and an umlaut.
: The German equivalent of the english form „than“ is „als“ and follows the comperative adjective.
English: 100 is bigger than 10
German: 100 ist größer als 10