Hello there, welcome to the forums.
I currently don't have the time to help you in detail, but the guide you're following is outdated and probably not useful unless you know what you're doing already to a degree (it also describes the use of mencoder, which is deprecated. You should use ffmpeg or x264 instead).
Instead follow
Wiki: EncodingGuide/PublicationManual, which uses a premade package that does everything automatically for you with a bit of setup. If you just want to practice you can stop after the "Encode the video" section. If you want you can upload your resulting Youtube encode somewhere (to show your logo and subtitles) and post them here too.
BTW: The error you receive comes from the fact, that either mencoder is not installed or the mencoder executable is not in your PATH:
https://en.wikipedia.org/wiki/PATH_(variable)
(I can't make that clickable or this post breaks)