Inversion
Used in formal English to make the sentence more emphatic or dramatic.
Usual adverbial expressions:
Not only did she win the championship, but she also set a new record. Not until he received the test results did he realize the severity of the situation. Never have I seen such a breathtaking sunset. No sooner did she finish her presentation than the audience erupted in applause.
We change the order of the subject and auxiliary:
Not until he received the test results did he realize the severity of the situation.
Not until he received the test results he realized the severity of the situation.
In present and past simple, we use the auxiliary + main verb:
No sooner did she finish her presentation...
No sooner she finished her presentation...
Compare:
Normal word order:
I have never heard such a ridiculous argument.
Inversion:
Never have I heard such a ridiculous argument.
Inversion should only be used occasionally for dramatic effect. Overusing it will make your English sound unnatural.