A router needs to be configured to the requirements of your ISP. The relevant information should be on their website. (Tell us which one it is and we'll try to locate it for you although, if you're where your username suggests, I can see that I'll probably need to call upon the Spanish I've largely forgotten since I stopped learning it 44 years ago!).
The actual way that you configure a router is to connect it to your computer with an ethernet cable and then enter the relevant IP address into your web browser's address bar. That allows you to gain access to to the router's settings panel. Since the IP address that you need varies between manufacturers, we'd also need to know the make and model of your router.
(The reason that my answer might seem to be in conflict with Rocky's, above, is that Rocky obviously received a router from his ISP that was pre-configured with the relevant settings).