First off, I'd like to say hi to all the moderators here. You have been doing an amazing job helping us English learners. I have been lurking on this forum for a while and this is my first post ever!

Okay, here are some of my questions:
I've heard people, especially younger peopel say a lot " I am/was like..." or "he/she is/was like..." I've never learned this kind of expression before. What does it mean?
And some other expressions: Plain Jane, Miss Goody Two Shoes(not sure if I put this down correctly). What do they mean?
Thanks in advance and keep up the good work!
elearner