If you are about to buy a laptop, make sure it comes with a built in wireless connection. The alternative is to fit a wireless PCI card or buy a USB wireless adapter. If your present broadband modem is a USB type, you will need to buy a combined modem/router, which you connect by cable to the filter on your 'phone socket. The laptop will then connect by wireless to the modem/router.
I am not sure, others will be able to advise on this, but you may need to initially connect your modem to the laptop by cable in order to set up and configure the wireless connection to your ISP. This will not apply if you also have a desktop PC, which is hard wired to the modem as this can be used to set up the broadband connection to the ISP. In any event, your modem/router will come with all necessary software and instructions on how to do this.