1) via the dashboard, we can select from a list or choose by name or other ways
2) via the dashboard, we upload a zipped theme fie or a plugin file and we extract
3) we FTP the theme folder, via FileZilla or another FTP program, to the /wp-content/plugins/ for plugins
and /wp-content/themes
Once you've located your WordPress installation folder, you can access the plugins folder by navigating to "wp-content/plugins" within your WordPress installation folder. This is where all your WordPress plugins are stored.
The themes directory is located within wp-content and is named themes . This is the directory that contains all the themes available on your website. Each individual folder in here is a separate theme
Before the installation take a backup.
In case of white screen remove the theme folder from the /wp-content/plugins/