This question would be better asked in one of the forums about software development.
Anyway, you are probably looking for the Process.Start method in System.Diagnostics. You can pass as an argument the pathnname of the autocad executable, and the process will be started. To send commands, you can use
Keys.SendKeys, which will let you "inject" key presses into autocad. But anyway, as I mentioned before, the Training and Certification forum is not the best place to get a detailed answer for that question.