WordPress is an open source tool for creating websites and blogs. It is by far the easiest and the most powerful content management system which is written is PHP. WordPress is popular among people who love blogging and designing. WordPress provides some inbuilt themes and plugins which are customizable. Now the question is what are these themes?
WordPress themes provide skin to your website or blog. These themes present your idea to your visitors. WordPress themes can be rendered as it is but if you have a brand or your own design you can customize the theme accordingly.
There are various themes which are available. They are either paid or free. The cost of a theme depends on the level of design and customizability of the website.
Free WordPress themes are available but because they are free, they may be common. If you wish to address a small audience then it is okay to use a free theme.
However, if you want to address a large crowd and publish your website your way you may want to purchase one of the paid themes.
Can you build your own themes?
Of course! With knowledge of HTML, CSS, JavaScript and PHP you can create your own theme. Apart from this you need to have basic knowledge of database and programming.
Conclusion:
Understanding WordPress is very easy but using it to create a website is a big task. But because it is open source and its documentations are available you may get all necessary help for building your own websites.