Like and as in some contexts can mean the same or similar, but in other contexts, like and as give the sentence very different meanings. To learn how to use the words, like and as, correctly, we should understand their  meanings.

like and as – defined

AS
Let’s look at the word ‘as’, for there are several way that this little word is used.
1. COMPARISON
AS + SUBJECT + VERB.
When AS is used as a comparison
I am not as good as she is
Nobody sings as she does.
They went to the party dressed as they were.
2.  DESCRIPTION OF A FUNCTION
Another use of AS is  as a way of describing a job, or the role or function that a person or a thing has.
He started his career as a carpenter.
I work as a tour guide
She used the tapestry as a decoration in her living room.
3. CONJUNCTION
As a conjunction, AS is followed by a clause containing a subject and a verb.
He became a writer, as his parents had been.
We all like Mary, as she is an interesting person.
4. AS IF
The verb after AS IF – also used as a comparison, is always in the past subjunctive, no matter what tense the sentence is.
She dances as if she were bewitched
He spends as if there were no tomorrow.

LIKE
1. Like is followed by a noun or a pronoun.
VERB + LIKE + NOUN / PRONOUN.
She speaks English  like a native.

LIKE vs. AS
Where like and as differ is when you mean that literally it/you/they are the subject, and when it/you/the are like or similar to subject
As the Principal, I think all students should attend the Annual Prize-giving Ceremony. (I am the Principal.)
Like the Principal, I think all student should attend the Annual Prize-giving Ceremony (I am not the Principal, but we share this opinion.)

LIKE, AS IF, AS THOUGH can all make comparisons.
You look as if you’ve been shopping.
You look as though you’ve been shopping.
You look like you’ve been shopping.

Like and as in some contexts can mean the same or similar, but in others like and as give the sentence very different meanings.