Walk is a verb, which means to take a walk or walk. In English, the third person singular form of a verb is usually formed by adding "-s" or "-es" after the original verb. For verbs ending in consonant +y, you need to change y into I and add -es. Therefore, the third person singular form of walk is walks, which means that the subject of the third person singular is walking.

In addition, the third-person singular form of verbs needs to be used reasonably with tenses, such as present continuous tense and simple present tense. At the same time, in practical application, we need to use different verb forms flexibly according to sentence context, subject and other factors.