Inversion 

The core mechanism: inversion means the verb (or an auxiliary verb) moves to a position before the subject, when normally it would come after.

English's default word order is Subject → Verb → Object (S-V-O). She runs. He is tall. They have finished. The subject always comes first, then the verb.

Inversion breaks that. The verb — or more often just the helping/auxiliary verb — jumps in front of the subject instead.

Watch what actually moves:

• Normal: She had never seen anything so beautiful. (Subject "she" → auxiliary "had" → rest)

• Inverted: Never had she seen anything so beautiful. (Auxiliary "had" jumps in front of subject "she")

Normal: The sun rose over the mountains.
Inverted: Over the mountains rose the sun.

Normal: Never had she felt so alive.
(Normal order would be: She had never felt so alive.)
Inverted: Never had she felt so alive.

Normal: A strange silence followed.
Inverted: Then followed a strange silence.

Normal: He is not only talented, but also hardworking.
Inverted: Not only is he talented, but he is also hardworking.

Normal: I have rarely seen such courage.
Inverted: Rarely have I seen such courage.