The positive is the simple, most basic form of an adjective. To use it in a comparison you have to use other comparative phrases before and after the adjective,
such as "so ... wie" ("as ... as"), to express that living beings or objects share a similarity or have the same level of a quality or qualification.
Other comparative phrases in German include "genauso ... wie" ("exactly as ... as"), "gleich ... wie" ("as ... as") and "nicht so ... wie" ("not as ... as").
The two beings or things being compared are always in the same grammatical case.

so + adjective in its basic form + wie

The comparative form shows a difference between the living beings or objects being described. The degree of the adjective can be increased by adding the suffix -er:

Example:
schlecht — schlechter.

There are also irregular forms. The comparative form of "gut", for example, is "besser".

The comparative word "als" (than) comes after the adjective. In the comparative, the living beings or objects being compared share the same grammatical case.

Comparative (Endung -er) + als

More:

Just like an adjective in its basic form, a comparative adjective can precede the noun it modifies, in which case it is inflected:

Examples:
Ich habe eine bessere Idee!
Professor Meyer ist ein besserer Professor als Dr. Anderson.
Ich habe einen schlechteren Test als du.