To partly answer your question - normally, like is used before a noun or a pronoun,
He runs like the wind.
She looks like me.
and as before subject + verb or a prepositional expression,
Nobody knows her as I do.
On Friday, as on Monday, we meet at eight.
However, in informal speech many people use like where as should be:
Nobody loves you like I do.
Like I said, she wasn't there.
Student or Learner