Hi, thanks for posting your question!
In the line
.:/home/nodejs/app, we are telling docker to create a volume in the container. The syntax to do this is
[source directory]:[destination directory], or stated another way
take this stuff
and put it here. So in our example, the
. refers to the current local directory. If I'm in the directory
. will refer to the contents of the
. If I'm in/home/bar
will refer to the contents of the directorybar
. The end result in our example is the contents of my application are created in the Docker container as/home/nodejs/app`.
Hope that answers your question!