So you have a computer aka a server connected to the Internet.  How do everyone know where you are and who you are?  It is through IP addresses.

You will find that your local Internet connection can’t do a proper job at web hosting.  Reason being, most ADSL lines or other Internet lines runs on dynamic IP addresses, that means the IPs keep changing for your computer from time to time.   So if you want to put a web site and email in your computer, this is the main problem.

For normal hosting companies, they have fixed IP addresses and their Internet connectivity runs far faster than your local home Internet.

What is an IP address? It is basically a set of numbers which computers recognized each other on the Internet.  Does not make sense if you want to look for your company to type http://203.81.50.138 etc right? You need a superb memory to remember tons of addresses.

This is when DNS, Domain Name System comes into play, a DNS resolve the IP addresses into human readable form for eg http://www.8.to instead of http://203.81.50.138.

For hobbyists normally they subscribe to something called Dynamic DNS systems which basically detects your IP changes if you are using home line and change accordingly.   But this is not typical for corporate or professional hosting companies.