This article explains how to connect a Wi-Fi extender to a router to improve the strength and range of your Wi-Fi network.
NETGEAR WiFi Extender Installation: How to Do It?
Before you can install an extender, you need to buy one. These devices come in many different shapes and price points, and many extenders are for a specific use, such as gaming or portability or range.
Once you have a Wi-Fi extender, you'll need to decide where you want to place the extender before you can begin the actual installation.
Placing your extender is largely about finding the sweet spot in your home: a spot that's close enough to your router that it can easily pick up your signal, but also far enough away that the network the extender creates can cover the space you want.