Read and remember.
Quite often in English, certain expressions with a negative meaning are placed at the beginning of a sentence. English speakers do this to stress the point they want to make. This usually makes what the speaker is saying more striking, original or surprising in some way. In order to make such a statement, inversion (обратный порядок слов) is necessary.
Not only do you have to go over the cross-bar, but you must go further each time since they lengthen the swing.
Вы не только делаете полный оборот вокруг горизонтальной оси, но и продолжаете крутиться дальше, поскольку качели с каждым разом удлиняются.
The same rule applies to:
rarely, seldom — редко, изредка
scarcely, hardly — только, едва ли, едва
never, never before — никогда, никогда раньше
no sooner — не раньше чем
