In order to create a workspace, one should run the following in the terminal:

$ mkdir -p ~/workspace_name/src
$ cd ~/workspace_name/src
$ catkin_init_workspace
$ cd ~/workspace_name/
$ catkin_make

The previous commands creates a workspace named workspace_name. Once a workspace has been created, it is important to source it in order to work with it:

$ source ~/workspace_name/devel/setup.bash