|Would have been helpful if you provided details of the make/model of your modem & router.|
The usual way to share an internet connection is to connect from modem to router WAN port and then connect each client system to a router LAN port. You have not indicated whether you want to connect the laptop in a wired or wireless manner, or even if your router has wireless capability.
Undoubtedly the router came with a user manual. Start by reading it.
Goin' Fishin' (Some day)