If you have a free, personal or premium plan, you cannot install third-party add-ons. You can, however, monitor your site's performance with statistics, optimize for search engines with essential WordPress SEO tools, or scan for spam and security threats, all without the hassles of installing and maintaining plugins. It may seem unfair to have to pay for a business plan to use WordPress plugins, but there are reasons why this is the case. When you upgrade to premium, you can access the add-ons, but you still cannot install them.
You can go ahead and install a free theme from the WordPress theme directory or upload a theme that you have purchased or downloaded from a third-party provider. If you use WordPress with another host, you can get these same features simply by installing Jetpack. Free add-ons often have the option of upgrading to a premium version that offers improved functionality. However, the more plugins you install, the more likely they are to affect the performance of your website.
The real power comes from WordPress plugins, free and paid extensions that add custom functionality to your website. If you're troubleshooting a problem or need to temporarily disable an add-on to resolve a problem on your site, it is possible to do so. There are more than 55,000 WordPress plugins available for download, so you can choose which ones to install depending on the specific needs of your website. Although WordPress comes with features for beginners without technical knowledge, gaining access to plugins and other files or folders can be a challenge.
To install a plugin, you must have the installable plug-in file saved as a ZIP file. If you encounter any problems with your zip files, contact the plugin developer for the final solution. Quality plugins will release updates from time to time to keep up with major WordPress updates. As a result, you'll have a wider range of file sizes to install the new plugins you need to improve your website.
That “bad format” message on your screen means that the native files you uploaded didn't come from the plugin developer.