':Like' means 'similar to': A crocodile is like an alligator. 'As' means in the role or capacity of: He works as a waiter in a restaurant. Compare these two sentences: 'Don't wear a Hawaiian shirt and camera in town - you look like a tourist.' This means that you resemble a tourist. You aren't a tourist, but people might think that you are one. 'You can visit this country as a tourist for a few months.' This means that you 'are' a tourist - it's is your official status on your visa. We also use 'as' for comparatives - 'Spanish isn't as difficult as Russian.'

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Like is a comparative. It compares two things which have something in common with each other. A soap bubble is like a balloon made out of water. It's an indirect comparison. As is used more as a direct comparison. I am as smart as my brother.