If you are creating a WordPress site for yourself, before you make any style customizations to your theme, it is very important that you create a Child Theme. If you don’t, the problem is that if you make any changes to your theme’s styles, the next time your theme or WordPress comes out with an update, the update may override your changes and you’ll have to add them back. This is assuming you made detailed notes of all the changes you made in the first place. WordPress updates generally fix bugs and make improvements, so you’ll want to stay current with WordPress updates. Always back-up your database before updating, in case anything goes wrong.

Instructions for how to create a WordPress Child Theme can be found at: http://codex.wordpress.org/Child_Themes. You will need FTP access to your site and your FTP login information (different from your WordPress login), which you can obtain from your hosting provider (such as GoDaddy or BlueHost). After you create and activate your child theme, it is important that you leave the parent theme installed, because the child theme will take most of its data from the original parent theme. You should keep your parent theme updated to make sure you have the latest bug fixes and improvements.