Saving Halo

I just downloaded the Halo Trial Version and I would like to know if there is a way to save the game and come back to the same spot at a later time. I know I can save the checkpoints, but I want to be able to turn off the computer, have part of a life and come back and pick up where I left off.

If you have the instructions, no song and dance, please. Just tell me how to do it in plain English.

Thanks for your help.

post this in free talk dude this is mod section