“what’s” is only “what is”.

You can only abbreviate “what are” to “what’re”, e.g. “What’re the chances of winning the lottery?”

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In everyday life, sure if you don’t mind saying stuff like, “Hey what’s you doing to tonight?” and “What’s those kids doing on my car?”

Not my thing, I think it sounds stupid, but I hear it all the time.

What is = What’s

What are = What’re

You can shorten the singular form. Is; for example:

“What’s that?” -(What is that?)-

Also the plural form: Are; for example:

“What’re you going to do? -(What are you going to do?)-

Usually -with only few exceptions- you shorten the plural form when its followed by: You, They, We.

Now, if you are talking in singular you cannot shorten it into plural or vice versa. You must keep it either singular or plural.