Hello again,
You insert the signal into the formula:
Vam=(Vc+Kam*Vm(t))*cos(2*pi*fc*f)
and then reduce to trig terms that sum. You end up with sum and differences terms of the carrier freq and the Vm frequency (or frequencies). You then draw a single line at each of those sum and difference frequencies who's amplitude equals the peak multiplier of that term, divided by 2 because that's how the trig functions reduce.
For the example they gave, you can see this in detail as they solved it completely. For a single cos signal you would only have one sum and difference to do, plus the carrier as they did in the example.
Here's an example with three cosine sources of different frequencies:
Vc*cos(2*fc*pi*t)
+(V3*kam*cos(2*fc*pi*t+2*f3*pi*t))/2+(V3*kam*cos(2*fc*pi*t-2*f3*pi*t))/2
+(V2*kam*cos(2*fc*pi*t+2*f2*pi*t))/2+(V2*kam*cos(2*fc*pi*t-2*f2*pi*t))/2
+(V1*kam*cos(2*fc*pi*t+2*f1*pi*t))/2+(V1*kam*cos(2*fc*pi*t-2*f1*pi*t))/2
Note that for the third one here, we would plot a line at the sum and difference frequencies with a height of kam*V3/2. If you examine the above you can see the pattern.