I want to know the difference between these 2 sentences.
As a mother, I warn you.
Like a mother, I warn you.
The first sentence is spoken by someone who is a mother. It could be rephrased "I am a mother and I warn you", They are speaking from the point of view of a mother.
The second sentence is saying "If I were a mother I would warn you" the speaker is not necessarily a mother or even female. They are saying what they think a mother would say.