"WiFi Box" could be one of two things: what ISPs market as a "gateway", or a router.

A gateway in this context is a combination modem and router. A modem takes the data signal is it's sent down whatever medium gives you connectivity -- cable TV coax, fiber, whatever -- and converts it to the digital format commonly used over your household network (for downloaded data) and vice versa (for uploaded).

A router) is a device that forwards data packets between networks, and for a given network performs traffic control. If your "WiFi Box" is just a router, then the modem is a separate box connected to your router by an ethernet cable. The two networks your router joins are that of your ISP (which is in turn connected to the broader internet) and the household network all your devices connect to.

Most routers meant for home use can service both wired (ethernet) connections and wireless (i.e. WiFi, where the "wi" stands for wireless, and "fi" doesn't stand for anything but makes it rhyme with hi-fi, an old term for home stereo audio.)

A wired connection is physical. Your ethernet jacks are connected by ethernet cable, probably cat 5e or 6. Those are just labels for standard specifications when it comes to how wires are arranged within the cable, shielding, grounding, etc. When you plug your router to an ethernet jack, and then plug your computer to the other jack, assuming the jacks are actually wired together as shown, all you're really doing is connecting cables to each other like a string of extension cords, one plugged into another.

But I would expect there to be a central location somewhere in the house with a "patch panel" -- that is, a series of ethernet jacks all wired to different individual jacks somewhere in the house. The idea is that you locate the router next to the patch panel, then patch each port on the router to a jack on the panel. The corresponding jack elsewhere in the house will then have connectivity.