How long should I expose the frame for a long exposure photo?

To start creating a long exposure you should set the shutter to stay open for at least 2 seconds. From here you can start to experiment and figure out what shutter speed works for the effect you want to create.

If you want to achieve roads with those blurred lights then leaving the shutter open for 30 seconds or more is the way to do it. If you want to try motion blur which is a good option for street and nightlife photography, try to make the shutter speed a bit shorter between 1/4 of a second and 3 seconds, and also move your hands to create that blur effect.

These techniques take a while for you to master but with time these will be useful to add to your arsenal of photography techniques.