It is considered dangerous to bring your queen out early because you can make a mistake and lose it.Or in order to prevent the loss you have to make extra moves and lose tempi.
second question: its good to know the most common openings because when you make a mistake in the opening phase you have to work hard to compensate.
YES it is necessary to learn specific openings to improve at chess. Just being able to ID the major openings and variations is a head start, eventually you need to be realistic enought to ditch the openings that don't work for you and find other ones that do.
It is often dangerous to develop the Queen prematurely unless you know what you are doing for instance 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 (NimzoIndian Defense) and now both 4.Qc2 (classical variation) and 4.Qb3 (Spielmann variation) are both sound. However when you develop the Queen prematurely without doing so in a "book" opening that calls for an early Queen development you will usually regret it if your opponent knows what they are doing.
YES it is necessary to learn specific openings to improve at chess. Just being able to ID the major openings and variations is a head start, eventually you need to be realistic enought to ditch the openings that don't work for you and find other ones that do.
It is often dangerous to develop the Queen prematurely unless you know what you are doing for instance 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 (NimzoIndian Defense) and now both 4.Qc2 (classical variation) and 4.Qb3 (Spielmann variation) are both sound. However when you develop the Queen prematurely without doing so in a "book" opening that calls for an early Queen development you will usually regret it if your opponent knows what they are doing.
Thanks for the help. One step closer to being decent at the game 
Your queen is a vulnerable piece like your king... but it does have advantages of being able to attack from range. I think less important than "you might lose it" is your opponent can gain tempi by attacking it, as it forces you to move your queen in response.
As for knowing opening lines... playing in an opening which you are comfortable in is helpful, and if you know the themes of the opening, you will gain points relative to other openings. However, I feel understanding opening principals, pawn levers, tempi, and control of squares is more important. I play a ton of blitz openings that I have no idea of theory past move 3.
Yasser Seirwan advocates some openings that are universal in response (Kings Indian Attack) as a good way to learn chess. You can play the basic moves there without knowning any theory.
Rules are meant to be broken ;) I had a game not long ago where I tried sending the queen out early(ish). Against better opponents I doubt it would be effective, but novices always seem to panic where the queens lurking about.
Quite simply ... would you walk your king out on the board in the beginning? No ... because even a pawn can attack him and force him to react/run. This would be bad because
1) You run the risk of losing your king/getting mated.
2) The more subtle reason => You end up reacting to your opponent in desperation and end up doing nothing else to help your cause, i.e. develop, bring your pieces out etc. It's like you gave your opponent a 1/2/3 move handicap.
Though in the endgame, you'd confidently walk your king out and use him as a fighting piece ... that's because your king doesn't feel like he's stepping over landmines each move.
The Queen, while all-powerful is no different in this aspect. The opening essentially allows both players to shape the landscape of the battlefield/terrain as quickly as possible to suit their pieces. You ever push a center pawn for free because you forced your opponent's piece to move away? Same story .... By giving your opponent a target like a Queen, he shapes his landscape for free because he's making you move it multiple times while he develops his pawns/pieces. Remember, any of your opponent's weaker pieces or pawns can threaten a queen and potentially force it to move away.
I've always thought of the Queen as a piece that looks for targets, not the other way around.
Though at the beginner levels, irresponsible queen attacks (1.e4 + 2.Qh5 + 3.Bc4 for e.g.) actually get you results because your opponents (also beginners) tend to have poor board vision and cannot see or accurately deal with threats on f7.
As the other posts suggest, novices tend to panic easily, so you get results!
These cheapo wins and a certain movie out there usually leads to this wacky notion that you can be this gung-ho desperado who brings his queen out into an attack hoping for a early knock-out. Once again ... against strong or even decent opposition, this is almost always a bad idea.
Unless the last stop on your chess bus is beating your uncle, dad and kids in your neighborhood and then retiring from chess, you really want to learn to play clean if you'd like to take on stronger players.
There are openings (like the Qxd5 Scandinavian) which require an early queen move. Likewise, if there's a tactic involving an early queen move (and by tactic, I do mean a forcing sequence leading to material, not a cheapo threat that you hope he won't see) , by all means, go for it.
Though as the other posts suggest, do not start looking into exceptions this early on in your development. Learn how to punish premature queen moves ... you'll start seeing the benefit of "free or tempo-gaining moves " and quickly figure out why you never want to rush out with your queen.
considered dangerous to bring out your queen early?
Also, is it necessary to learn specific openings to be good at chess?