hi sima, below is a network diagram of how to connect them
Your internet service provider provides you with a a Modem. You connect the modem via wire or usb cable to your Wireless Router.
Your Wireless Router has wire ports that you can use to connect desktops, you can also use the wireless on your laptop to connect to the wireless router.
If you can provide us the brand and model number of your wireless router, we can check on its user guide to see the specific details -- how to setup a wireless password, and how to diagnose if it is working properly.