help me with these sentences

1)Here is an example of using being in "the" be + being construction.
2)being is a present participle used to form "the" progress tense with is
Why have we used "the" in the sentences

3)When being is used with "A" past partciple, it is "A" passive construction.
Why have we used "A" here and why not "the" like in the first two sentences?