1) Pre-Production - All the planning involved before you start filming. For example writing a script, casting actors etc, scouting a location, filling out all the necessary forms, preparing costumes/props etc. 

2) Production - The actual shooting of your video. Lighting, sound, special effects, getting the camera shot right etc.

3) Post Production - The work done after the film has been shot. For example editing the video, adding and mixing music and audio, additional extra's such as ADR (Additional Dialogue Recording), visual effects etc.