The training suggestions above by @chyna are good. If you go to school and pay for it, you can make the money back relatively soon. A company training program will also be good, and you will end up with the same credentials, with a little experience to boot.
As far as to buy your rig or not, it depends on your expectations for the career. If you’re going to do it “for a little while”, you probably will not pay off a tractor in just a few years, unless you drive a lot and find an extremely lucrative contract. If, however, you want to pursue the career long-term, owning your own rig will give you a certain amount of autonomy. It will be your business, you will own the assets (the rig, etc.) and will be ultimately responsible for all maintenance. I’ve known some drivers who eventually expanded to own two or three rigs, which they then leased out to other drivers, or hired other drivers to drive.