There are different tools available for creating your website. Depending on the extent of your knowledge of HTML, JavaScript etc. some will be more suitable than others.
Having created a site, you will want to improve it by adding features such as counters, guestbooks, feedback forms, chatrooms, feedback forms and a whole host of other "features".
So you have a fantastic site and all your mates know about it. How many visitors to you get every week? 3?, 5?, 10?
Why not more?
Simply because nobody else knows of its existence. You need to tell people that your site exists. Not just that, but tell them what it is about.
How do you find a new site for the first time? - probably by using a search engine.
You need to tell the search engines that your site exists - they will tell anyone looking for a site covering the same subjects as yours, that there are lots of appropriate sites INCLUDING YOURS !
Building and maintaining a website can take up a lot of time. There is also some expense involved - such as purchasing a domain name, hosting fees, editing and design tools, licences for graphics, photographs and images etc.
Why not recover some of that expenditure through advertising on your site?