Adjectives can take one of three nifty forms:
Positive. For when you don't want to make or imply a comparison.
Comparative. For when you want to compare two things.
Superlative. For when you want to compare three or more things.

Here's a nifty table with some examples:
| POSITIVE | COMPARATIVE | SUPERLATIVE |
|---|---|---|
| low | lower | lowest |
| stale | staler | stalest |
| blue | bluer | bluest |
| old | older | oldest |
| lively | livelier | liveliest |
Click below to see positive, comparative, and superlative adjectives in context.