For a website to be visible to millions on the internet, it has to be online. Therefore, web hosting provider will put your website in a computer which is connected to the internet and you website can get reach by anyone who has access to the internet. This computer used by hosting providers are the same as your computers at home but the have set it up to serve your website need. Hence they are called servers.
Web hosting providers will have very fast internet connection provided to their server that hosts thousands of websites. They actually rent out the space they have in their servers to clients to have the space on the World Wide Web. Big companies will have their own group of servers in their own possession while smaller companies usually rent servers from the bigger companies.
The web hosting companies usually provides many choices of hosting plans for you to choose from. They may differ in their features with different requirements to adapt to your needs. For the basics, the bandwidth will always be a monthly limit. It is the amount of data which is transferable from you hosting computer to the millions out there connecting to your website. Therefore, the more bandwidth you have, the more stable your website is going to be because your website is still able to support the amount of traffic coming and going from your website. However, if you exceed your limit, you will either have to pay extra fees or see your website break down.
Therefore, be extra careful when you come around some company that claims that they provide unlimited bandwidth. It is actually a marketing trick to attract users to fall into their trap. They provide unlimited but you have to pay for whatever extra bandwidth that you might use once your original limit is up. So, select with care when you are deciding on a hosting provider.