If you click on the "Map Services" button in the toolbar, there should be two options: Map Selected or Map All Services. (Unless you are one an older version of TVH? You haven't said ...)
The TVH documentation actually does a pretty good job of explaining muxes/services/channels, but maybe this will help:
A mux (or MUltipleX) carries multiple streams. These streams can be programs, video, audio, teletext or other miscellaneous data. A collection of these streams (such as a video, 2 or 3 audio, and a teletext) would be a single service. Often, broadcasters will duplicate a service on different muxes, so the same service can be found on 2 or 3 different muxes. TVH allows you to group these duplicated services into the same logical channel.
The advantage to this is that a tuner receives a full mux, meaning that all of the services on that mux input, but when you watch a particular channel, TVH filters out the unnecessary ones. However, if for example you have 2 muxes: 1 carries ABC, NBC and CBS; and 2 carries NBC, FOX and PBS. (Yes, I know the example is contrived, but play along ...) If you wanted to watch FOX, the tuner would be set the mux 2. Now, if you have a recording scheduled for NBC while you are watching FOX, the tuner can use the same mux it is streaming FOX on to also receive the NBC feed and record that, without having to stop FOX and switch muxes.
Hopefully this clears it up a little bit, and helps explain the mux/service/channel split a bit. However, I recommend checking out the documentation, because it has a much more thorough explanation.