The following table is a brief overview of the essential differences between using WordPress.com versus downloading a package from WordPress.org and then installing it on your own server:
| WordPress.com (online platform/service) | WordPress.org (open source software) | |
| Installation | No need to install anything; just sign up. | Install WordPress yourself, either manually or via your host's control panel. |
| Themes | Use the themes made available by WordPress.com (https://wordpress.com/). | Use any theme available anywhere, written by anyone (even by yourself). |
| Plugins | No ability to add third-party plugins. | Use any plugin available anywhere, written by anyone (even by yourself). |
| Upgrades | WordPress.com provides automatic upgrades. | You have to upgrade it yourself when upgrades are available. |
| Widgets | Widget availability depends on the available themes. | You can widgetize any theme yourself. |
| Maintenance | You don't have to do any maintenance. | You're responsible for the maintenance of your site. |
| Advertising | No advertising of your own allowed. However, WordPress.com itself sometimes runs ads on your site. | You can advertise anything and in any amount you like. |
| Ownership | Even though the content belongs to you, WordPress.com can take down your blog at any moment if they consider it to be inappropriate. | You have complete control over your site, and no one can force you to take it down. |
| Domain | Your site is available as a subdomain under .wordpress.com by default, but you can also upgrade to a paid package and use your own, manually registered domain name. | You can use any manually registered domain name. |
Overall, WordPress.org is a much better choice for those who want to learn how the WordPress platform works and how to use it to build optimized and versatile websites. WordPress.com might be a better solution for those who simply need a website fast.