When Harry heard these words from Professor Dumbledore at his Welcome Feast in First Year, he wasn't sure how to react. The world of Hogwarts, and indeed the Wizarding World at large, was still a mystery to him. Harry wondered how serious Dumbledore was. He wondered also what exactly he had gotten himself into.
The first years among you may well find yourself in a similar position. You have Met the Ministry, matriculated, and most importantly, survived the sorting ceremony with only a few mishaps. Some of you have even participated in the first task of the Triwizard Tournament. But even as you start to adjust to life at Oxford, you might find yourself lost in this unfamiliar city, with its unfamiliar people and unfamiliar vocabulary to boot.
Well, let me tell you that you're already headed in the right direction: you've joined a society (or perhaps several), you've made it to third week in one piece, and you're reading the Quibbler which, if I may say so myself, says a lot about the excellence of your literary tastes.
So you don't know what a trashing is yet, or you're still trying to figure out why some people get gowns with sleeves and the rest of us don't. You'll learn. Maybe you haven't found a perfect study spot. Or maybe you're still struggling to find your friends. Whatever it is, remember, it's ok. Sometimes, you'll find what you're looking for when you least expect it.
Be brave, be kind, be ambitious, and try not to do all your work the night before. Embody the best that Hogwarts has to offer, and I promise you, you'll be just fine.
As Dumbledore would say: "To our new students, welcome, and to our old students, welcome back! Another year full of magical education awaits you."