If you can't get to the starter or the main connections on the starter.... then honestly you can do much. Do you have a stick or automatic? That was never answered.
On an automatic, in order to start it you would leave the car in Park, Ebrake if you'd like too. Then turn the key to On, like it's running. Then you'd jump or bridge on the solenoid on the starter (& this cranks the starter) the little wire on solenoid to big post positive power on the solenoid.
Essentially, you are using the always HOT or Positive wire from the Battery to power the little post/ignition switch wire. Since they are next to each other on the solenoid, this is usually the easiest place to jump. So it'll crank for as long as you jump the two connections... and you basically want to let go once vehicle starts. You can use insulated alligator clip jump wire to do this. Maybe 14 gauge at the littlest (if you understand wire gauge). I hope this helps explain "how" it works.
If you have a stick, it's a similar procedure, but make sure Ebrake IS ON & NOT in gear.