Wireless networking (or Wi-Fi) is a convenient way of getting an Internet connection to devices around your house, but it is rarely a perfect solution.
Wi-Fi uses an Access Point (AP) to talk to your device. The AP is normally built into your router but could be separate, and this turns network data into radio frequencies and sends them out over the air. Your device receives the signals and turns it back into meaningful data.
Modern APs and routers use WPA2 encryption to make sure your information is scrambled while in the air, but older devices may only support WPA or the older WEP encryption; this can cause compatibility problems if you get a new router.
Advertised Wi-Fi transmission speeds are a bit of a con and can never be achieved in real life: Every packet of data is transmitted twice to the far end, compared, and if they do not match they are sent again, twice. So the actual achievable speed is always less than half the advertised speed.
Wi-Fi was originally built to handle emails and internet-browsing traffic and for this use it is not a problem to have a few delays. Our more modern needs for video and audio streaming puts a new burden on Wi-Fi , firstly by forcing giant amounts of data over the air, but those data really need to arrive at your device at the right time. Any delays to the data’s arrival and you get buffer-face.
So what causes these delays? Usually it is interference in the radio spectrum; other Wi-Fi networks can interfere such as your neighbour’s router, or sometimes other wireless things like thermostats or audio equipment can interfere. I have even seen issues with energy saving lightbulbs or fridges giving out weird radio waves and killing Wi-Fi Signal.
Imagine having a conversation in a quiet room: it is easy to hear and you can speak quickly and be understood (high bandwidth.) Now move that conversation to a busy pub with music playing and many people shouting… you now have to slow down and speak louder, often repeating yourself and hearing things wrong (poor bandwidth and high lag.) This is what happens when there are lots of other Wi-Fi networks near yours.
In summary: Wi-Fi is good for basic browsing and email, but if you use Wi-Fi for streaming video then consider trying to use a wired connection instead to stop saturating your radio airspace. Sometimes you can connect a cable between your router and TV or computer. If it is a long distance or awkward route then you could ask an electrician to run a cable around your house or through the walls.