Since you're brand new to the place, I recommend dusting.
Methodically start at one end of the store and dust. But while dusting, pick up and look at each and every item. Read the description of what it is and what it is for on the back/front of the package. Ask someone if you still don't know what it is for. Make your way around the whole store, dusting and reading and picking up and looking. At least once a week, when you come in, repeat the process. It'll get a bit faster, but that way you'll be able to identify new product, or if someone has moved something from one spot to another.
In that way, you will get to know the stock. If someone comes in and asks for whatever, you'll be able to take them right to it.
If one of your coworkers is changing a window display or other in-store display, get involved and help them. Ask if you don't know what things are for.
Many manufacturers send along brochures about their products. In quiet moments when you're not dusting and when there are no customers in the store, read those brochures.
Become familiar with the catalogues (online and paper) which your shop uses. If you don't have something in stock, you should be able to flip right to that section in the catalogue and look for it quickly. And learn how the ordering works ... can you make special orders, do you have to wait until you've reached a certain dollar amount. That way you'll be able to give the customer a realistic idea of how long it would take to get the item in.