Inversions are used to make sentences more formal, they are not so much used in spoken English as written but they do appear in the use of English and writing parts of the exam.
Never, seldom, rarely, hardly, Not until, at no time, under no circumstances, at no point, little
Never have I been so angry with a person like I am with you right now.
The meaning of this: I have never been ………..
All conditional sentences can be manipulated and you can change their word order. In formal usage, you can also use inversions.
Were the teachers at the school better trained, problems like these wouldn´t occur.
The meaning of this: If the teachers were trained better……………