Welcome to Gaia! ::

Yes, there are very different rules. In a nut shell:
1. You play with 99 cards in your deck. With the exception of Basic Lands, you may not have more than 1 copy of any card. This is called a "Singleton" format.
2. You must choose a Legendary Creature (not a Planeswalker) to act as you Commander/General. The Commander's colors determine your deck's "color identity", and what cards you can play.
3. You may not have cards outside your color identity. For example, if you Nicol Bolas as your commander, you may only build your deck with Blue, Black, and Red cards. They also cannot have abilities that require anything outside that color.
4. Your Commander is not part of your deck, he stays in a special "Command Zone", where you can cast him from at any time you normally could cast him from your hand. So if you had Teferi, you could cast him at Instant speed. If they die or get exiled, they go back to the Command zone. Beware! Each time you cast them, it costs an extra [2] mana. And if they get bounced into your hand or deck, they stay there.
5. Each player starts at 40 life.
6. if you take 21 damage total from any given Commander, you lose.

There are other rules, but that is what you need to know to get started. As far as how you should build them, that's still a hotly debated topic. Some say it should be a strictly Casual format and that we should refrain from anything too broken. An emphasis on design rather than function, flashy over forceful. Others say that the format opens up so much to us, that you shoudl build to win just as you would any other deck.
I myself keep two. I have a hyper-synergistic Sharuum the Hegemon deck that has multiple wincons and an aggressive tutor and ramp package to power them out. This is a tournament deck.
I also have a Skithiryx, the Blight Dragon deck I use as a Casual Griefer deck for late nights at the kitchen table. (It should be noted that both Mono-Black and Poison are bad EDH ideas unless you know the people you're playing with won't severely beat you.)

Oh, I see.
And by 'broken' you mean like... Serra Ascendant?
How many people normally play in a match?

Officially, Coalition Victory is banned. Most games are played with at least 4 players, although formats like Emperor with anywhere from 6-18 can be played, time and interaction increasing of course with each player added.

EDH games with 3-5 players don't typically take all that long if everyone is paying attention and tries to play as speedily as they can.

One informal rule that really helps speed gameplay is: If you are going to tutor or rearrange your deck at instant speed, do it immediately upon ending your turn instead of waiting for the player to your right's endstep.

This is bad strategy competetively speaking but that rule comes with an informal agreement not to take advantage of people because they're trying to speed up the game.

Yeah, it's not competetively optimal play but trying to play EDH competetively in multiplayer quickly devolves into unfun stupidity so there's little point and there are few things as annoying as waiting for 5 minutes while someone tutors and shuffles and then have them say, "ok it's my turn now..."

I, personally, prefer not to ban anything beyond the official list. The vast majority of cards can be dealt with fairly easily if everyone packs enough answers.

Ward of Bone and Felidar Sovereign are good examples. Neither is especially hard to remove and if a player can stick a 6 cost permanent and protect it for a turn or so against the rest of the board, they deserve to win.

Ward of Bone can be abusive with Sunder or Armageddon effects but at that point you're talking about a multiple card combo in a highlander format and, in any case, there are dozens and dozens of abusive comboes in EDH.

What I would object to is someone playing Ward of Bones and Sunder or Armageddon and then having no way to win the game. However, I see that as a seperate issue from the card itself. Locking down the board and not having a clear win is just rude and stupid but I see an out of game solution (I.E. say "dude, if you do that again we will stop playing with you.") as more effective than trying to ban every card that can create a lock.

A strong and clear social contract and a like minded group of players are key to a good EDH experience but you can say that about pretty much any competetive, multiplayer, game.