Video explanation
A color CRT cutaway connects the electron guns, deflection coils and phosphor screen. Slowing the scan from real time to individual points reveals how a moving beam builds an apparently continuous image line by line.
Electron beams excite phosphor
Electron guns produce beams that make phosphor glow on impact; beam current helps control brightness.
Deflection creates raster scanning
Deflection coils steer the beams across successive lines, with blanking normally hiding retrace.
Refresh forms the visible picture
Phosphor persistence and visual integration make rapid scanning appear as a complete picture. Slow motion is an observation aid.