Learn German: Das Mädchen wird rot. - The girl is turning red.

The verb werden means to become or to get. While English uses different verbs for a change of state (like turning red, getting tired, or going bald), German simply uses werden for all of them.

Why is the verb spelled wird?

The verb werden is irregular. In the present tense, its stem vowel changes from an e to an i for the du and er/sie/es forms. Since Das Mädchen is a third-person singular subject, it takes the form wird.

Wait, why is it Das Mädchen (neuter) and not feminine?

Any German noun that ends in the suffix -chen is automatically neuter and takes the article das. Because Mädchen historically means little maid, grammatical rules make it neuter, even though it refers to a female person.

Why doesn't the adjective rot have an ending here?

Adjectives only take extra endings when they are placed directly in front of a noun. When an adjective comes after a linking verb like sein (to be) or werden (to become), it stays in its basic dictionary form.