The gradable adjectives can be modified with the words such as very, too, and enough:
very bad, too bad, bad enough
The gradable adjectives can be used in the comparative and superlative forms:
small, smaller, the smallest
bad, worse, the worst
beautiful, more beautiful, the most beautiful
The non-gradable adjectives can not be modified with words such as very, too, and enough. They also can not be graded which means they cannot be used in comparative and superlative forms:
dead, alive, finished, unfinished, amazing, etc.