There are 3 ways to install a WordPress plugin.
Automatic Wrodpress Plugin Installation
Manual Wrodpress Plugin Installation
Manual Wrodpress Plugin Installation via FTP
1. Automatic Plugin Installation
As name suggests, Its automatic.
Go to plugins in back-end.(must have permissions)
Click add new. You search, download and install plugins from official WordPress library here.
2. Manual Installation
If you have downloaded archive file(zip only), then same as automatic installation, go to plugins. Now click add new and upload file. WordPress will install that plugin for you.
3. Manual Installation via FTP
If you have downloaded archive for the plugin, extract it.
Now, Access the path “/wp-content/plugins/”(without quotes) and upload the extracted folder there.
Go to the plugins in the back-end and you will see that plugin there in the list with all other installed plugins.
You need to activate the plugin before using it.