There are many uses for both words. For now, I will assume that you are asking about using "like" as a conjunction. Most grammarians will tell you that "like" should never be used as a conjunction. The conjunction for those types of comparisons should be "as" or "as if".
Like can be a preposition. It therefore can take an object:
That pear tastes like an apple.
John looks like his father.
However, like shouldn't take a clause.
[incorrect] He plays golf like he was playing baseball.
[correct] He plays golf as if he were playing baseball.
[incorrect] Winston tastes good, like a ciagrette should.
[correct] Winston tastes good, as a cigarette should.