Videos PlugIn

Can anyone help?
I am trying to upload .avi video to my site.
I have WP Video Posts PlugIn but I keep getting this message….

“FFMPEG is not installed on the server, therefore this plugin cannot function properly.
Please verify with your administrator or hosting provider to have this installed and configured. If ffmpeg is installed but you still see this message, specify the path to ffmpeg installation below:”

I have absolutely no idea what this means and how do I rectify it – completely new to all this!

Can anyone show me what to do?

Many thanks