After plugin is installed and activated it works straight away. But, sometimes, with advanced plugins you will have to do some more job to get plugin working properly. So, it happens, that after installation you will see on left hand side of admin panel some new icon. This is a kind of plugin management icon. Click it to see plugin’s management area and what plugin’s settings are available. Often in this plugin’s panel you will find description of available plugin’s settings. Read the description carefully before you use plugin’s short codes or change plugin’s settings. However, it happens, that sometimes plugin’s description is hidden in readme.txt file. Radme.txt or read-me.txt of something like that can be found in Plugins->Editor option in WordPress admin panel – you will need to select installed plugin to see plugin’s files and edit manually readme.txt after you find it. This is a bit headache solution, but I write about it in case you will not see any plugin’s description straight after plugin installation.
In some cases plugin’s management options can be hidden under a different admin panel menu option, like, for instance under Tools or Settings. Check it after plugin installation and after admin panel page is reloaded.
Other possibility is that installed plugin comes with Widgets. In such situation you will have to use Appearance->Widgets option in admin panel menu. You will see some new widget, so drag-and-drop it to suitable place in your WordPress theme layout. The plugin widget can work straight away, or works with defaults settings which can be changed within widget itself. For instance, your simple shop plugin comes with shopping basket, and you can place purchase buttons anywhere in your pages, all works correctly, but, shopping basket is not visible as long as you don’t drag-and-drop widget basket to suitable place in Appearance->Widgets area.
So, to put it together: plugin management can be hidden under a new icon in admin panel menu, under Tools or Settings in admin panel menu or/and additionally under Appearance->Widgets of admin panel.