Every sentence contains two main parts: subject and predicate.
If the sentence is a command, it may contain only one word. For example, Hurry! is a sentence. Hurry is a verb. The sentence is a command. The sentence is about the person being told to hurry. The subject is understood to be You.
To write good sentences, you also need to learn these additional terms:
The best way to teach (and to learn) the parts of the sentence is to take your time and get in plenty of practice with exercises.