As verse Has ?

in simple terms, as is a comparison word - he works as a fireman, the drink is as cold as ice, etc. Has describes a possession - he has a dog, she has a cold, or it describes events in the past (he has finished his dinner) or events that are ongoing (she has been a doctor for ten years).

There has been refers to something either singular or uncountable (there has been a mistake, there has been corn growing here for years), and there have been refers to more than one thing (there have been eight kings named Henry, there have been ten elections in my lifetime). . Always look at the noun to (mistake, corn, kings, elections) to help you decide whether to use has or have.

"as" and "has" are totally different words that do not share any of the same meaning.

As for "there has been" versus "there have been" – "has" is singular, "have" is plural.  But this is not always true.  "has" changes to "have" when used with a modal verb (would, could, should, must or the future (will).  And "has" is the third person conjugation (he/she/it) when used in the simple present tense. "have" is all others  (I, you, we, they...all "have").

You just have to learn it. It takes repetition and exercises to learn a language. This is especially true for English verbs, which are notoriously misunderstood by non-native speakers.