Congrats on your new boots! Right out of the box your boots will have a durable water repellent (DWR) finish on them which, along with the Gore-Tex lining, will keep water out of your boots. You should not need to re-apply a DWR to your boots for a while, depending on how often you use your boots. When the time comes, we recommend a footwear cleaner and DWR treatment for leather, such as Nikwax.
In the meantime, purchasing a stiff bristled brush, like the Sof Sole Boot Brush, that you use to clean off debris from your boots after each use will not only keep them looking good, but also prevent any dirt or grit from penetrating down into the leather and affecting your boot's performance.