There are thousands of free and premium WordPress themes available today, and you can use any of these WordPress themes to make your website look great. But using an available theme also has a disadvantage that its not unique. Your website looks exactly like hundreds or thousands of other websites using the same WordPress theme.
One way out of this is to get a custom WordPress theme for your blog. It may not be a viable option for many of us as custom WordPress theme development costs a lot. Another way to make your site unique is to customize your generic WordPress theme to make it unique.
You can apply many WordPress tweaks and optimization to your theme to give your site a new look. But you must either hire a WordPress developer or do all the tweaks yourself. If you want to go on the DIY (do it yourself) path, you must have a basic knowledge of how WordPress themes work.
Don’t worry its not very hard. You can learn the basics of WordPress themes from the info-graphic below which is published by Yoast. Refer to WordPress codex along with this Anatomy of WordPress themes info-graphic and you’ll know enough about making basic customization to your WordPress theme.