I am not the author of this plugin, but :
This plugin works with something that is called a SHORTCODE.
since it appears that this plugin does not provide a widget , and assuming you have almost no programming experiance in wordpress, you can do one of the following :
1 - You need to put the shortcode [front-end-upload] inside a post or page . just copy and paste (with the square brackets) . there is no need to be affraid of nothing . In this case the upload "form" will be displayed in the specific post (or page ) where you have pasted it . you can also add normal text like any other post / page .
2 - If you really want it to appear inside a WIDGET , you will need to enable SHORTCODE execution in your widgets, and then paste the SHORTCODE ( [front-end-upload] - remember ?? ) Inside a TXT widget .
Now , in order to be able to do that option, you can either :
A - use another plugin for shortcode execution , like this one :
B - copy the following code , and paste it inside your theme file that is called functions.php .
add_filter( 'widget_text', 'shortcode_unautop');
add_filter( 'widget_text', 'do_shortcode');
This code will enable you to use shortcode inside any normal text widget. (I never really looked , but I guess these two lines is more or less what that plugin from the previous option is doing .It is that simple.)