To better undersatnd:

to download tomcat: docker pull tomcat:latest

to run tomcat: docker run -d --name mytomcat -p 8080:8080 tomcat:latest

to change to the container that you create in this example "mytomcat" is the NAME of your tomcat: docker exec -it mytomcat /bin/bash

to move files between folders for backup: mv webapps webapps2

at last to copy the files that are missing in "webapps" folder from "webapps.dist": mv webapps.dist/ webapps

exit

I hope it helps.