syntax query

currencyExchangeHelper = CurrencyExchangeHelper::newExchangeDate(currentLedgerRecId, this.TransDate);

What does this line of syntax mean ?

It will create an object of the class, by using that static constructor(newExchangeDate).

By doing so, you can access its members (methods).

Syntactically, it calls a static method with two arguments and assign the result to a variable.

Kranthi already explained the purpose of the call.

I would just be careful not calling it a static constructor; that’s something else. newExchangeDate() is a method.