Usage(two common expressions)

NOT ONLY, BUT ALSO
~ used to emphasize that something else is also true. "Not only" links two words or word groups referring to things, actions, or situations. You put not only in front of the first word or group, and but also in front of the second one. The second thing mentioned is usually more surprising, informative or important than the first one.

This structure is usually “balanced”, so that the same kind of words follow "only" and "also".

Bertrand Russell was not only a philosopher but also a physicist.
(not only + noun, but also + noun)

My boss is not only smart but also hard-working.
(not only + adjective, but also + adjective)

Wilhelm Furtwangler not only conducted the orchestra but also composed the music.
(not only + verb + object, but also + verb + object)

My piano teacher not only plays the piano, but also the violin. (not balanced)
The above sentence is not exactly wrong but many people consider the style is bad. (at least in academia)

For emphasis, you can put “not only” first in the sentence, followed by “be” or an auxiliary, then the subject., then the main verb.
This structure with inversion can sound formal and literary. It often adds emphasis to the negative.

Not only did we lose our money but we also lost our pride.
Not only men but also women were chosen. (not inversion)


ONLY IF
~ used to say the only condition in which something can happen or is possible.

I tell you, but only if you don’t tell anyone else.
This company will succeed only if it has good products to sell.

In formal English writing, "only if" and its clause can be placed first in the sentence. In the second part of the sentence, "be" or an auxiliary, comes before the subject and the main part of the verb.

Only if I get a job will I have enough money to go to university. (inversion)

"Only if" is a common expression of inversion, to state the condition for a particular situation to happen.
e.g. Only if you study hard can you get good results.

"Not only,...but also" is a common expression of inversion also, to introduce another situation apart from the first situation.
e.g. Not only can you read books in the study room, but also discuss with your classmates and friends.