It may mean that one of the packages in the dependency chain cannot be installed.
One of the dependent packages is freeglut3-dev
This is from the ubuntu universe repo.
If you have not added this repo, it will not be installable, and you will get this message about “cuda : Depends: cuda-10-0 (>= 10.0.130) but it is not going to be installed”
To solve this particular example (freeglut3-dev), add the ubuntu universe repository (google that), and install freeglut3-dev:
sudo add-apt-repository universe
sudo apt-get update
sudo apt-get install freeglut3 freeglut3-dev libxi-dev libxmu-dev
To debug the issue more generally (if it is not due to freeglut3-dev), you have to chase the dependency chain. Each time it says a package is not going to be installed, add that package to your install line, eg.
sudo apt-get install cuda-10-0 cuda-toolkit-10-0
and keep this process up until you get to a package that can’t be installed.