Step-1: On your WordPress dashboard, navigate to “Plugins” and then click on “Add New.”

Step-2: Search for the type of plugin you want to install. For example- you’re thinking to install a plugin for the contact form.

Step-3: If you found your desired plugin, click the button “Install Now.”

It will take a few seconds to install. Wait until it finishes installing.

Step-4: Once it’s installed, click the button “Activate.”

That’s it for installing and activating a plugin.
In most cases, you’ll find an additional menu on your WordPress dashboard after installing a plugin. From there you can use your plugin features to add additional things to your website.
If you installed any apps from ‘Google Play Store’ or ‘Apple iTunes’ on your phone, think of the plugins as your website apps. Plugins enhance or add some extra features to WordPress.
How to install custom or premium plugins
Step-1: Once you download the plugin in a zip format, go to your WordPress dashboard, navigate to “Plugins » Add New.” And then click on the button “Upload Plugin.”

Step-2: Choose your plugin file (zip) and click “Install Now.”

It will take some time to upload.
Step-3: Once the upload finishes, click the button “Activate Plugin.”

That’s it for uploading & activating custom/premium plugins. In this same manner, you can also download any free plugins from the WordPress repository and upload them as well.
Any questions, let me know in the comment.