Themes are the core aspect of website customization and offer the ability to control the customer-facing view of WordPress to greater or lesser degrees.
1. Login to your WordPress Admin Dashboard.
2. In the right sidebar, hover over Appearance, click Themes, then Add New.
3. Browse the list and click Install, or upload the theme files downloaded from third parties.
4. Click Activate.
Themes often specialize in a type of website, such as blog, photography, portfolio, etc but many themes offer advanced functionalities and options for customization, often behaving in some ways like plugins.