For example, the simple adjective "tall" can be inflected with comparative -er to make its comparative form "taller".
Note that this only applies to gradable adjectives; it is illogical for absolute adjectives to have comparative forms, though real life is messier than logic. Note too, that this suffix can only be inflected onto shorter words usually one or two syllables; longer words cannot have this added and are therefore defective adjectives. We use the adverb "more" instead.
There are sometimes minor spelling changes, particularly the doubling of consonant letters, e.g. "big" -> "bigger".
To make the superlative form, we can add superlative -est.
This suffix is pronounced with a /ə/ (schwa) vowel sound. In accents with rhoticity the subsequent /r/ tends to be pronounced; in non-rhotic accents the /r/ tends not to be pronounced unless it precedes a vowel sound in the next word, when a linking /r/ is often used.