Sometimes I feel I should no flag newbies or new users. Should I comment instead and ask them to explain better? ...or should I leave this to the moderators?
If you find a post that needs to be flagged, flag it independently from who posted it. Whatever the post was created from a new user, or from a 10K user, a post that should be flagged still needs to be flagged.
As for leaving that to moderators, moderators don't go hunting for bad posts; they just act on posts that caught their attention in some way (such as when a post is flagged), or on posts that are blatantly wrongs, such as blatantly off-topic questions.
There are cases where a flag should not be used, such as for:
- Asking a moderator to judge the correctness of an answer
- Asking a moderator to edit a post, if not in the case sensible information is revealed
- Asking a moderator to down-vote a post
- Asking a moderator to change a comment into an answer