I would like to buy a semi truck and start my own business, but I don't know what I need to do to get started. Can you help?

Are you currently a truck driver working for another company?

If not, go to work driving a truck for someone.

There are a lot of companies that off lease purchase and/or drive to own trucks. ( and if you are in the trucking business you would know most of them, since you see their adds in all the truck stops)
But they will require experience in the trucking business.

Next of course you will have to use some company to get your loads, or get a contract with some company to drive your truck for them.

Fr. Chuck had some good points. It would be easier to go to a company that allows you to lease with them, it gets you in a truck and a lot of companies have a no-strings attatched policy. You can get out of it if you change your mind and you don't have to worry about selling a truck. What country are you in?