@Charles H. In its simplest form, you need to form the LLC with the Secretary of State, get a Tax ID, and create/sign an operating agreement. At this point, you will have a recognized and functional LLC. On an ongoing basis you have to do your annual filings to maintain the LLC, keep minutes and records for the company, and ensure that you maintain the key business necessities (bank accounts, insurance, etc.) to show that this is in fact a business. Your state may have some requirements that I am not aware of, but normally this is about all you need to create an LLC.
Just keep in mind when you start to own properties in an LLC, you are now operating as a company which means commercial lending, personal guarantees, pass through taxation, and all of the other considerations of being involved within a company and not personally holding these assets. @Christopher Smith is correct that you can hold these assets pesonally and mitigate risk through other means, but really is up to you and what you feel is best for your situation.