Once you have completed your flight planning, you may file a flight plan if you desire. Pilot's flying under visual flight rules are not required to file a flight plan. However, filing and opening a VFR flight plan means that air traffic control is aware of your flight. In the event you do not close your flight plan within 30 minutes of your estimated time of arrival, they will know you are overdue at your destination and initiate search and rescue procedures.
Opening and closing a VFR flight plan is sort of like telling the flight service station that you are heading out on a trip, and you'll call them when you get there to let them know you made it okay.
Flight plans can be filed over the phone, on the internet, or even while airborne. An example of the flight plan form can be found in chapter 5 of the AIM.
Once airborne, contact the flight service station on the appropriate airborne frequency to open your flight plan. Flight plans are normally closed by telephone or over the internet after landing.
It is easy to forget to close your flight plan. Make sure to make a note or checklist item to remind yourself to close your flight plan, otherwise search and rescue procedures will be iniated 30 minutes after you were expected to land.
If a flight plan is filed and never opened, the flight service station will assume you planned to fly, but decided not to take the flight.
ยง 91.153 VFR flight plan: Information required.