As discussed, installing plugins is slightly different from Themes. All you need to do is head to
Plugins > Add New
You can then search for specific plugins in the search box in the top right hand section. When you find the correct plugin, all you need to do is install and activate the plugin.
This may take you to a separate page where you will need to fill in details for the functionality.
WARNING : I will go through most plugins that are vital and won’t change the functionality of your site. If for any reason your site does not function the way it is supposed to, then there is normally a challenge with the plugin (and it’s normally the last one that was installed, or there has been an update) If this does happen, simply update all of your plugins, and in most cases this will solve the challenge.