Most of the questions on this site about staying on either side of a long-stay visas are about people who do not need a visa for short stays in the Schengen area (like US or Australian citizens for example). Rules for people who do need a visa, like Turkish citizens are more restrictive.

Your type D visa probably has no maximum duration of stay (but only a period of validity) and isn't controlled by the Schengen regulations so staying before up to 90 days elsewhere in the Schengen area before the start of your time in Poland is perfectly fine from that point of view. The time spent in Poland under the type D visa does not count towards the [90-days-in-any-180-day-period limit]( and you would therefore never exceed it.

But you need to have the right to enter the Schengen area in the first place. As a Turkish citizen, this means that you need a visa. Your type D visa exempts you from this requirement and would therefore also allow you to visit other Schengen countries, *but only after the start of its validity*.

You don't necessarily need to enter Poland first or to go there immediately so you could in principle tour the Schengen area for some time before starting your studies. So if your visa starts before the beginning of the courses at your university, you might be able to squeeze some vacation in-between. But you cannot avail yourself of your type D visa before its first day of validity.

Theoretically, you could also apply for a Schengen visa to cover your vacation. It's perfectly legit and having a long-stay visa starting right after the end of the vacation should in fact help you a bit (as you don't need to prove you will return to Turkey) but it means starting another application from scratch, with all the hassle, the fees, etc.

(Also pay attention to the formalities required by your student visa, some countries require long-stay visa holders to undergo a medical exam or registration with the local authorities within a certain time of entering the Schengen area.)