We've been given some practical work on ROS, but the instructions were focused on ROS Electric and rosbuild, so we spent some time trying to figure out how to use catkin and its workspace mechanism.

mkdir -p workspace/src
cd ./workspace/src
catkin_init_workspace
catkin_create_pkg myPackage roscpp ## Add dependencies, separated with spaces here, like: std_msgs rospy ...
# Time to do stuff here, like creating a main or whatever...
cd ./myPackage
vim ./src/main.cpp
# Time to add our file to the build list
vim CMakeList.txt
# Let's say from here, that's we've name our executable myExec
cd ../../
catkin_make

Now, if you want to be able to use you workspace with rosrun and stuff _without installing it, it's time to source another setup.bash, source workspace/devel/setup.bash

Time to run rosrun myPackage myExec