Noticing Newbies

Well I knew it wouldn't take long to do something wrong. Only two days. I posted my first review on a poem and really liked it so I gave it 5 stars. I read that I was supposed to be honest, encouraging and supportive. I thought I was. I didn't see anything wrong with it, and it had a good story to it, but it appears after the email I received following my review, I should be sticking to a 3 - 3.5 star. So encourage them but not too much, because we can all improve? Still not sure I understand the entire review thing. I read a story yesterday that had a lot of grammatical errors, and the story was slow and weak, even though I thought the story line could be a good one. I thought about giving that one a 3, but then didn't do anything because I thought it might be too harsh. So now I'm confused and gun shy to do another review.