A time machine is a machine that can move you in time backwards or forwards.
Space Time Machine
If you travel fast enough, you will be slowed down to the point where you will think thay 70 years equal only 1 year.
Still Time Machine
You get in the chair and travel through time.
Handheld Time Machine
You can use these to travel through time anywhere.
In 1921, Harold Harkinian illegalized time travel because it made things go haywire. He created the Time Travel Police to fix the parodoxes. Although many people still use it illegally, including Weegee with his Weegee Time Machine.