Blogs are just a way for people to post comments on the Internet for others to read. Some blogs are long with lots of information and some are short. Think about columns you read in newspapers, they are often done as blogs also or the writer may just put short amounts of information in a blog as ideas appear.
Anyone with Internet access can do a blog. Quite often you will hear people use WordPress to do blogs but that product requires a more technical ability to set up and maintain. So unless you have the expertise or someone who will help yuou may not be best
A popular blog site used now is blogspot by Google. You create an account and then you create or post blogs. There is a space for the subject line and then text. It is very similar to email. Lots of people are using it. You can look at a blog I am doing there of a trip I am talking out west. I write each day on what I did. People can choose to read or not and blogspot is free. http://dwighttravelwest2011.blogspot.com/
An older product that I also use is yahoogroups.com It sets up a little differently but you can also email messages to it that are posted. I have used it since about 2000. I have a couple blogs there http://sports.groups.yahoo.com/group/ibbgcm/ and http://groups.yahoo.com/group/Watt-Thoughts/
With a blog you can tell the world what you think and you can allow people to respond.