The container is a runtime instance of image. If you are familar with object orient programming, the image is similar to the class and the container is an instance of class.
The easiest way to run a container is to use the docker run command.
docker run -it --rm -name dotnet mcr.microsoft.com/dotnet/framework/runtime:4.7.2-windowsservercore-ltsc2016 powershell.exe
This command will initiate a container named dotnet based on the dotnet Framework runtime images, execute the powershell.exe as its main process and provide the interactive tty to the user.