can be found by reading the Self Help Center guide.  It also was asked on this board in the past week or so.  The experienced hobbyists who provide assistance here will never be rude to a newbie, but we do get frustrated when people ask questions like this without doing the most rudimentary homework, so please do some reading.  You will no doubt have more questions but if you do some homework they'll be much less frequent.  The Self Help Center is at the top of this board next to the life preserver.
Now, since I'm being a nice guy while swimtrekker (the host of this board) is sick, here's your answer.
Meet & Greets, also called mixers, are parties hosted by well known mongers and/or providers.  They often take place in hotels, but sometimes are held in private residences.  They are an excellent way to meet providers you're interested in seeing and checking them out "up close and personal."  Sometimes there is sex, sometimes not, although providers and players will often hook up at a M&G and leave together for a session.  I've seen it happen. But screening is very similar to that which a provider does before seeing you.  So, as a newbie, you need to build up your credentials the usual way (and please do some reading on that, too).
There is a Meet & Greet Board here that you can go on to read the announcements of M&Gs being set up.  All in all, these can be really good events.
Personally, I love M&Gs but prefer it when they are Meat & Greek.
Good luck.

The one so called M&G I attended was just 7 of my closest board buddies meeting for a night of dinner and clubs in Manhattan, but it was not some big party full of hookers and hobbyists. I don't find these things discreet at all, and who knows what pics will be snapped of you without you knowing it. There is a certain board that loves to post pics from these meet and greets with names to go with faces...can we say HELL NO if you're married!

The bigger ones charge a rate for the guys usually and the girls are free. I have heard of lavish parties in upscale hotels where no sex is allowed, and I have also heard about the raunchy sex fest that happened at a Jersey one a while back. If I wanted to fk in front of a room full of people or blow in the bathroom for next to nothing,  I would be a swinger, not a hooker.

It just depends on which ones you attend and the people and things that are involved. You may love em or hate em depending on your tastes.

1. They are simply large cocktail parties for the most part, usually in a nice hotel meeting room, with drinks and hors d'oeuvres.  

2. The purpose to meet other hobbyists and providers in a normal civilian type setting.  There are no illegal activities taking place there.

3.  The men are usually charged a fee to cover expenses of the host/hostess, with the ladies being admitted free.

4.  What happens is you just mingle, talk, have a drink, and maybe make arrangements to see a provider after the party, or at another time and date.

5.  I have been to a few, but not really interested in another as they are pretty much the same people I have already met.  I know enough providers to make dates w/o going to a MnG.

Swim

Like a cocktail party. An opportunity to meet men and women who are in the hobby and perhaps even to get to know a provider whom you might want to meet for a BCD session at a later time. I have been to a few and they are really quite pleasant. I would say, go to one and decide for yourself if you want to attend others.

I have been to one in Atlanta so far and like some said....it was just a big cocktail party giving you a chance to meet some of the local girls without having to book with them. Gave me an idea of if we would click or not. Ended up meeting a few great girls there. But now later at night the party did get a little wild but was told those people would not get an invite next time and that it did not normally happen. Guess you will always have a few bad eggs to weed out of everything. Would I do it again....Probably....but also I'm single. As London stated may be more concern for the married guys attending. But over all the party was pretty under control. Plus you can always leave if it gets uncomfortable for you.....