As and like are often confused in English because we use them both to talk about things that are similar.
In American English, like is often used as a conjunction (instead of as), but the conjunctive use of like is not correct.

AS

It’s a CONJUNCTION. It should be followed by a clause containing a subject and a verb.
The structure of the sentence is usually: AS + SUBJECT + VERB

EXAMPLES

• He runs as a gazzelle does.
• Nobody plays tennis as he does.
• She’s a good singer, as her mother was before her.
  

As can also be a preposition, but with a different meaning from like. The meaning of as in this case is: ‘in the position of‘; ‘in the form of‘, etc.

• Last year, I worked as a secretary in my brother’s office.
• The news of her death came as a great shock.

LIKE = ‘similar to’; ‘the same as’; ‘for example‘(= such as).

It’s a PREPOSITION. It should be followed by an object to make a prepositional phrase.
The structure of the sentence is usually: VERB + LIKE + NOUN / PRONOUN / -ING. You can also say ‘like (somebody/something) doing something’.

Examples:

• It’s hot in this room. It’s like an oven!
  
• He speaks like a native speaker.
• He runs like a gazzelle.
  
• The floor has been polished. It’s like walking on ice!
• It sounds like a dog barking.