The following is my personal opinion:
Be verb: it is a copulative verb, which means "yes"
According to the change of time, be can be divided into the following categories:
Modern tense: am (used with I) is (subject is singular) are (subject is plural)
Past tense: were subject is plural and was subject is singular.
Future tense: wil be
wait for
Preposition: Prepositions are often used in nouns, such as in at on upon.
Adverb: A word, usually an adverb, that modifies verbs and adjectives.
Present continuous tense: a tense, in short:
Say the past, past tense;
Say the present thing, use the present tense;
Say things in the future, use the future tense;
For example: 1. She is an excellent girl in Beijing.
She is a good girl in Beijing.
Is is a be verb.
In is a preposition.
Extreme is an adverb
2. She is playing.
The tense of this sentence is the present continuous tense