Walking is the normal way for Sims to get around. However, in The Sims and The Sims 2, player-controlled Sims cannot normally walk from one lot to another. Instead, they have to get a taxi or use a car[TS2:NL]. Visitors to residential lots, whether invited or random, will walk when entering or leaving the lot, as will townies and neighborhood Sims who appear when Sims visit community lots. In addition, all NPCs in The Sims, and several in The Sims 2, will walk onto and off of a lot.
In The Sims 2: University, college students walk when going to classes or to take final exams. The Sims 2: Bon Voyage introduced the ability to walk between lots, but Sims cannot walk from a community lot to another lot unless they walked to that lot. The Sims 2: Apartment Life allows schoolchildren to walk to school and older Sims to walk to work.