Sometimes the word is meaningless. Sometimes, "it's like" = "the situation was" "He/she is like" = "he/she said" "I'm like" = I said / I thought "So she's like, 'I don't DO that sort of thing!' and I'm like, 'yeah, sure!'" As Barbara said, much of the time it is filler, much like "you know"

In most cases, when young people use 'like' in the way you describe, the word can be left out of the sentence without changing the meaning. E.g. I was like waiting for the bus when it started raining. I wouldn't bother learning how to use it as I think it is just trendy to speak like that and I'm sure it will drop out of use. It is definitely not good English.

I blogged about this very subject two years ago. Here is what I wrote: SATURDAY, DECEMBER 18, 2010 TITLE OF BLOG ENTRY: "Y'know, LIKE, uhm, LIKE, give me some time to think" So, I was LIKE on the bus, and LIKE two 20-somethings were talking, or trying to talk. And I LIKE whipped out my notebook and started scribbling. It was mostly the girl talking LIKE this and the guy occasionally mirroring her. 1. I thought LIKE . . . "like" = "maybe"; adverb 2. He's LIKE . . . / He was LIKE . . . / Some of them were LIKE . . . "like" = "I'm paraphrasing what he/they said" "like" = "saying" (progressive/continuous tense - "to be" form + -ing verb) The speaker is communicating that what she is about to say may not be exactly what was said, that it only comes close to what was actually said. This implies hesitancy, timidity, or the lack of an adequate vocabulary to express what she would really like to say. 3. a. Y'know, LIKE , . . . b. I don't think/know . . . he, LIKE, . . . c. It was, LIKE, . . . "like" = "uhm" The speaker has some idea of what she wants to say, but her mind can't come up with the words quickly enough to express it. 4. . . . LIKE crazy. Intensifies or emphasizes the following adjective; an adverb. 5. But I was LIKE . . . , I was so mad. "Like" has been replaced by "so," a more specific adverb. 6. Not LIKE that. "like" = "similar to"; preposition 7. Y'know what I'm saying by that? The speaker is trying to get the listener to reassure her that he understands or can guess at what she is trying to say. When I shared my notes with a friend, she said that this was the reason she paid attention to what she said to her young daughter and how she said it. And a child with an attentive parent who values what that child has to say isn't going to grow into a young adult who struggles for self-expression.