One may not leave 'his place' on Shabbos.
Mi`D`Oraysah one may go up to 8000 Amos from the edge of the city one is in. Chazal decreed that one may only go 2000 Amos from the edge of the city one is on.
Males and females
In Masechtas Eiruvin
That we should know that the world is a creation, it wasn't always there. Since Hashem created it in six days and rested on the seventh, it is appropriate that we too rest on Shabbos and not travel, other than walking for relaxation or enjoyment. Walking less than 8000 Amos is not tiring.
If one transgresses
If one goes even 1 Amah further than 8000 Amos, he receives Malkos. If one goes more than 2000 Amos, Bais Din may give him lashes for not listening to Chazal.
According to the Ramban
This is not a Mitzva Mi`D`Oraysah at all. The entire prohibition is Rabbinic in nature.
אל יצא איש ממקומו ביום השביעי
שמות טז כ