There's basically two ways to do it. Either you buy carpet already molded to fit your car, or you buy cut yardage and fit it to the vehicle as you go.
If you choose the custom route, you will have to do things like the transmission tunnel first with a separate piece of carpet, and then fit the flat areas up to the tunnel and either sew the carpet together or bind the edges. Go slowly, don't let the carpet move around, and don't make a cut unless you're absolutely sure. I'm sure the internet has videos of carpet layers fitting carpet on a floor in a house. Watch something like that to get fitting and cutting tips. There are threads on binding carpet right here if you search for that topic.
No one lives forever, the trick is creating something that will.