Hi
To answer a few of these points:
The vertical scale on the scans is something called brightness temperature. Radio astronomers use it as a measure of brightness (signal strength). It is given in temperature units (Kelvin) because we say teh sigbnal is the same strength as would be given out by an object of that temperature. To explain further, you will know that as you heat a metal bar, say, it starts to glow and as it increases in temperature the colour works through the spectrum from red to blue. The spectrum produced by these sort of opaque objects is called a blackbody. Our bodies are at a temperature that means we glow in the infrared. Most stars are hot enough to glow brightly in the visible. However some things are so cool they glow most brightly in teh radio part of the spectrum.
Now, in fact, here we are looking at a combination of radio waves from electrons spiralling around in magnetic fields and from hydrogen atoms in interstellar space. So the temperature in this case doesn't correspond to a real physical temperature but is just a measure of the brightness.
You should now start to see the plane of the Milky Way Galaxy as the bright ridge running along the middle. Superimposed on it we're gradually starting to see brighter spots as the blanks get filled in. We may need to adjust the scaling on the map to see both bright parts and faint parts to get the best view. It is these bright spots that we'll look at later.
Now to answer the question about why a spectrum showed 3 peaks rather than just one. Here the main peak in the spectrum is from hydrogen atoms producing emission at a frequency of 1420.406 MHz (about 21cm in wavelength). You see 3 peaks near this frequency because there are 3 clouds of hydrogen atoms in that direction each moving a different speed relative to us. This means the peaks are doppler shifted to different frequencies. Clouds moving towards us are shifted to higher frequencies (blueshifted), those moving away to lower frequencies (red shifted). Try changing the horizontal axis to velocity to see what speed the clouds are moving at (negative velocities mean they're coming towards us).
In fact, although one observation can't prove this, the 3 clouds are actually the line of sight cutting through three spiral arms! One is teh local arm in which our Sun sits, so it's velocity relative to us shoudl be about zero. The others are more distant arms. With a series of these observations we coudl map out teh spiral structure of the Milky Way, but maybe we shuodl leave that to another day!
All the best,
Tim