Plugins are the utilities that provides additional functionality to wordpress applications.To install the wordpress plugins you just need to put the plugin files to the wordpress folder wp-admin/plugins.After you have moved the plugin files to that folder you may want to activate it from the wordpress dashboard by going to Plugins menu and find the plugin and click on Activate.
In wordpress 4.9.5 you can install plugins directly from the wordpress dashboard.Just go to Plugins click on Add new.Search the plugin on the search box.Then click on install and then activate it.Done!
The deletion or removal is also easy in most of the cases.Simply just remove/delete the plugin files from the wp-admin/plugins folder you would like to uninstall it,It will be automatically removed from wordpress admin plugin area.Or you can just delete if from plugins area by clicking on Delete button.
You should always bear in mind that not all plugins easy to install or even removing them.Plugins can make your site go crazy if something goes wrong.So I would suggest be careful before adding or deleting any plugins.
So I would like to suggest always to refer the documentations of the plugins and wordpress,even the theme!Have fun.Good luck!
You may also like to read How To Move Or Create a Copy of Your WordPress Website