An operating agreement is a document that sets forth how the LLC's business will be conducted.  Among many other things, it describes how money will be distributed, percentages of ownership, what happens if someone leaves the business or dies, and each owners rights and responsibilities.  An operating agreement is best created in a roundtable discussion between owners.  If you discuss how things will be handled in the future, many disagreements can be avoided down the road.

There is not a requirement that you have an operating agreement.  If you are a single member LLC it is not extremely important to have one but some sellers will ask to see one before extending credit on business sales so you should probably have one. A single member LLC operating agreement can be quite simple and doesn't need to be longer than a few pages.

All multi-member limited liability companies should have an operating agreement.  The members of the LLC should get together with a sample operating agreement and go over every provision and decide how it will apply to their business.  The most important part of this exercise is not the resulting operating agreement, its the process of sitting down and deciding how the company will operate.  It is surprising how many people go into business together without talking about simple things such as how profit will be distributed and how company decisions will be made. 

You can find operating agreements for sale on the internet for usually around $15-20 dollars.  They are provided free of charge here!!! Check the upper left hand corner of this page for link.