I don't know what you have been looking at! From what you put, you have very little understanding of electricity, so if so, PLEASE get help from someone who does, before you hurt yourself or your equipment!
I'm assuming you are thinking about DCC control,
not ordinary dc 12v.
It would be easy to explain if we could post pictures on here, but -
From the mains wall socket to the transformer is one cable, but it has three wires inside it, in a flexible tube. DON'T MESS WITH THIS! Mains electricity can
kill!
From the transformer to the controller there are probably two wires, coloured red and black, or it might be a single cable ending in a plug of some description. Inside the cable are two wires. (That depends on what transformer and controller you are
using).
Your controller probably has six connections on the back, not counting the one for the power from the transformer.
It will have two connections to go to the track, two connections to go to the programming track, and two connections for lights
and such, around the layout. Again, it depends on which controller you have. Ignore the last two sets for now.
Now - the bus wires.
First-off, if you only have a small track, (that doesn't mean 'N' or 'Z' gauge!) you don't need this, just the two
supplied wires from the controller to the track.
The bus wires are two thicker wires, (provided by yourself), that run all around the track underneath the boards. (Thicker wires 'lose' less electrickery than thin wires). Each piece of track on the board
has two short thin wires that drop down through it, (fitted by you), and connect to the bus. All it does is by-pass any possible bad connections between pieces of track, and 'evens out' the power that reaches your loco's.
You have to make sure that all
the connections to the bus are the same way round!!
Get a piece of paper, and draw on it, one red ink circle, and one black ink circle, one inside the other. That's your imaginary track. Now draw a red line across the bottom, with a black line next to
it. That's your imaginary bus. Picture your two circles are made up of small sections, as the track would be, and join each section to the bus - red to red, and black to black, and then transfer the image to your layout.
If you get one (or more) crossed
over, the controller will see a short circuit, and turn itself off, so you have to take care to get it right.