If you are looking into importing a method from the Core.jar into your code, first of all, place the Core.jar into the dist folder. After than, look for a list to import "the library" Core.jar, which you can google. Once you do that, try to open the Core.jar with Winrar and see the folder. It could be like com.something.something, when it comes to its folders. this is how you can import it into your code. I am not sure however if this is what you are looking for.
Please read the rules before you create a topic. You placed your topic on the marketplace, where other people advertise that they either want to buy or sell, while your topic is related to a l2 discussion rather than a sale. I have also fixed your prefixes!