Torstennnn,
get a sheet of paper and paint my example as a graph.
Put OAT on x-axis and speed (IAS) on y-axis.
Then draw in my example above (one curve for 0ft and one for 10000ft).
The speeds in my example were in kt IAS.
Each curve consists of a flat part at lower temperatures and then a falling part at higher temperatures.
The edge denotes break-point temperature.
This gives you a rough example of VMCG on a jet powered airplane.
VMCA looks similar to VMCG, with the speeds a bit higher.
I hope that helps a bit