Since it seems a lot of people don't know that some of these answers are available in game under "Help", I thought I would post them here as well. This won't answer all of your questions, but should help

WHAT IS A CO-OP?
A co-op is a group of players who get together to chat and help each other in game.
The Co-op Building is unlocked at level 19, and you can rebuild it to create your own co-op or join someone else's. Co-ops can have up to 30 members.
Fellow members can exchange crops and goods with each other, letting them develop their towns faster.

HOW DO I CREATE MY OWN CO-OP OR JOIN AN EXISTING ONE?

The Co-op Building is unlocked at level 19, and you can create your own co-op or join an existing one.

Use the tab in the Co-op Building to create a co-op:
Creating a co-op costs 1,000 coins. Chose your co-op's name wisely, as you won't be able to rename it. Then choose a unique badge and co-op type:
Open: Other players don't need your permission to join your co-op.
Closed: Only players you invite can join your co-op (Bear in mind that you can only invite Facebook and Game Center freinds into your co-op.
By Request: Players send a request to join your co-op that you can accept or decline.

There are a number of ways to join another co-op:
Choose one from the list of co-ops in the Search tab.
Search for a co-op name in the Search tab.
Accept a freind's invitation in the Inbox tab.
Visit the town of a friend already in a co-op and learn more about it by tapping the Co-op Building in their town or the co-ops's badge next to their name at the top of the screen.

HOW DO I INVITE FREINDS TO MY CO-OP?

If you are a Leader, Co-Leader, or an Elder in your co-op, you can send invitations to other players. No other co-op members can do so.
You can only send invitations to your Facebook or Game Center friends. To send an invitation, go to your friend's town and then tap the button in the bottom left-hand corner with your co-op's badge. The invitation will automatically be sent to your friends Inbox, and then all you have to do is wait for them to accept it.

HOW DO I JOIN A DIFFERENT CO-OP?

You can only be a member of one co-op at a time. If you are already in one, you will have to leave it before you can join another.
To leave a co-op, tap the Co-op Building and then the Leave button. Once you've done so, you'll be free to join another co-op or create your own. Just bear in mind that if you switch co-ops too often, you will have to wait awhile before you can join a new one.

HOW DO I REQUEST AND GET GOODS FROM OTHERS PLAYERS?

You can only exchange goods with fellow co-op members.
Tap Request products to request goods, select the product you need in the pop-up window, then tap Request. The amount you can request depends on the product type and how difficult it is to produce. Don't forget what level your fellow co-op members are at when requesting a product, as they may not be able to send you what you're looking for. We recommend that you first chat with co-op members to figure out which products you will ask for, as you can't change your request. Instead, you will have to wait three hours before making a new one. There are help counters displayed in you co-op member list that show how many products each member has donated. The help counters are reset every seven days.

WHAT POSITIONS DO CO-OPS HAVE? HOW DO I CHANGE THEM?

The different co-op positions available help manage the co-op as a whole. There are four positions available at the moment:

LEADER: This is the person who created the co-op and can change its settings. The leader can invite new membersto the co-op, promote and demote them, and promote another member to the position of Co-Leader.
CO-LEADERS: These are members that help their Leaders, as only Leaders and Co-Leaders can promote members to this position. While they can do almost everything Leaders can, Co-Leaders aren't allowed to demote or kick the Leader.
ELDERS: These are members that can invite other players and accept or decline requests to join the co-op.
Leaders and Elders are in charge of deciding who will be in the co-op and monitoring the chat.
MEMBERS: These are the rank-and-file players, and they can request and donate products and interact in the chat. Members can be promoted (they just have to ask the Leaders or Co-Leadera to do it for them).

HOW DO I RENAME MY CO-OP?

Unfortunately, co-op names are permanent. Choose your name wisely and avoid using any offensive workds or personal information. We may consider renaming your co-op if you contact our Tech Support for one of the following reasons:
The name contains personal information you don't want to disclose
The name contains offensive words.

WHEN DO I GET FOUR-LEAF CLOVERS FOR HELPING OTHER PLAYERS?

Four-Leaf Clovers are given randomly, so you can't earn them by donating a certain product or by filling a certain number of requests. Players can receive no more than five four-leaf clovers a day.

HOW DO I REPORT OFFENSIVE ACTIVITY?

Even though we're absolutely sure that Township players are all friendly and polite, any community may have a number of people, deliberately insulting others.
This game has a system that filters profaniity and other offensive phrases when players create their towns and co-ops, and chat with others. However, there's always a way out to avoid any filter.
If you come across an offensive word, please take a screenshot of it and an offender's town and report it to our Tech Support. Remember that you can create a 'Closed" or "By Request" co-op, which would help you choose polite and reliable members.