Only if expresses that one condition is required to achieve a desired effect. (=SOLO SI...)
When used at the beginning of the sentence the auxiliary verb from the main clause is moved before the subject. (INVERSION)
Only if you dry your dishes with a towel, will they be spotless!
Only if you clean up your room, will you find your lost jeans.
Your windows will be clean enough to see your face only if you wash them with Zing!
I will please my mother-in-law only if my house is clean.
I am happy only if you are here. / Only if you are here, am I happy.
She was happy only if we told her what she wanted to hear.