When to use the present ordinary form of verb?

The "present ordinary form" of a verb is a bit of a confusing term. It seems to be referring to the base form of the verb, which is the form you find in the dictionary. Here's when you use the base form of a verb:

1. In the present tense, with the following subjects:

* I (I walk)

* You (You walk)

* We (We walk)

* They (They walk)

* Plural nouns (The dogs walk)

2. To form the simple present tense, third-person singular:

* He (He walks)

* She (She walks)

* It (It walks)

* Singular nouns (The dog walks)

3. To form the infinitive:

* To walk

4. After modal verbs:

* Can walk

* Will walk

* Should walk

5. In imperative sentences (commands):

* Walk!

Important Note: In some cases, the base form of the verb might be used in a different tense. For example, in the simple past tense with the verb "to be":

* I was (not "I am")

* You were (not "You are")

* He/She/It was (not "He/She/It is")

It's important to remember that the base form of a verb is the foundation for building different tenses and forms. Understanding its use will help you construct grammatically correct sentences.