The main idea is that you play as a Black Mesa scientist/employee who picks up an undamaged HECU kit and fights their way to the surface, in an effort to escape Black Mesa Research facility.
The HECU deployed in the Depths have locked up most blast/fire doors to halt the alien assault. To progress to the storage areas, these blast doors need to be opened, despite the threat of the aliens.
Also sorry for the overload of yellow/orange lights. There are plenty of other coloured lights in the map so don't worry.