Walking, driving, or any form of traveling can represent:
The passage of time, or making progress or moving forward in life
A transition to show a separation or passage of time between topics portrayed in a dream (for example, in a dream where you are walking from your office to your home, the walking portion could represent the separation between your work life and your home life, or it could represent the actual time between a real-life workplace event you're dreaming about and an event that happened later on at home)
Moving along your life path
A real-life activity, such as in a dream where you're exploring something that happened on an actual trip or walk recently