This sentence was used by Radio Shack in a commercial as an example of an incomprehensible instruction manual. This is really an extremely simple sentence and an extremely poor example. This was actually written by someone who spoke the English language. Many instruction books for electronic products made in other countries are written in the language of that country, then translated very poorly, probably by people who do not know the language they are translating to, but were simply given a translation dictionary.
Unit XLT-735B is a VCR. An RF converter is the component of the VCR that converts the VCR's output into a television signal on one channel of an antenna-type output. VHF 3 is the channel that output goes to, channel 3. Basically, this means that in order to view the output from your VCR, set your television to channel 3.