There are several ways to do this, depending on how your network is configured.
Generally, if you have only one router - you connect the network jack of your cable modem or DSL modem to the WAN ("wide area network" or "internet") jack of the router with a CAT 5 network cable or jumper. Each computer's network jack would be connected to one of the router's (4) LAN ("local area network" or "home network") jacks labeled 1, 2, 3, & 4. In the picture above, the left most jack (WAN) of the router connects to the cable or DSL modem. The "LAN" jacks labeled "1, 2, 3 & 4" connect to each computer's network jack in your home.
The above would change if you are simply adding this router to extend an existing network. You'd likely be using this router as a switch, and leaving the routing duties to the main router. Over simplified, all the CAT 5 network cables would be connected to the 4 LAN jacks. There would be no connection to the router's WAN jack because the output of the first router provides only private IP addresses used in YOUR location. The internet IP address from your ISP is used only at the first router so that your entire home has the single IP address. The WAN jack is for internet addresses only - and the LAN jacks are for local / private addresses in your home only.
Have a look at the LinkSys
web site for help configuring your particular model router, or reply with the model and version here.
I hope this helps & good luck. Please rate my reply - thanks!