Wi-Fi is common for most households but good Wi-Fi is not. Most homes have a single Wi-Fi access point and it may or may not be in the best location for adequate coverage. There is a lot of misconceptions about Wi-Fi products so let's see if I can't clear a few things up for you.
First, we need to go over the basic components of a WiFi network.
It is common to replace a router with built-in WiFi (WiFi router) with a new and improved model. That may be a good option if you are experiencing drop-offs and connection issues, but if all you need is better WiFi in an particular section of your home, a better upgrade maybe adding an additional WiFi Access Point (AP) to supplement or extend your network.
The most basic function of a router is to keep internet traffic isolated between two networks. Only traffic authorized to enter your home network is allowed in and only internet devices (clients) authorized by your router are allowed to communicate on your network. Wide Area Network (WAN) ports are the outside or incoming ports. Local Area Network (LAN) ports are inside your network.
If you have read Home Networking 101 I suggest you do before continuing.
Internet data plans from your Internet Service Providers (ISP) can vary greatly. Most plans are sold by how many MegaBits Per Second (Mbps) they can deliver into your home. Here is a general list of requirements for various activities.