Most routers use a default WiFi network name (SSID) that is hard to identify and remember.
Deep inside your router settings, you are able to change the channel that your router broadcasts its signal. 2.4GHz and 5GHz are the most common frequencies for routers.
The Edimax WiFi adapter is popular because it's small, cheap, and most common pi distros come with the drivers already installed. Setting this up via the command line is simple.
If you have a website running on your computer that you typically access by visiting http://localhost, you can also access this site from your mobile phone as long as both computers are connected to the same network.
There are many factors that can affect your Wi-Fi speed, and unfortunately there isn't one single remedy for all situations.