What is the correct way to install ROS pakages??

edit

You can just clone them into the catkin_ws/src folder.

Yes it is, catkin_make is the way to build your workspace within ROS, you can also compile one or multiple packages:

$ catkin_make --pkg "my_package_name"

Or

$ catkin_make --pkg "package 1" "package 2"

And you can compile your package manually:

Check this link for more

EDIT:

From dornhege remark:

$ cd catkin_ws/src/
$ git clone "Put the link here"
$ cd ..
$ catkin_make