...
Left click on the object you want to be the parent first.
Press the CTL key (OPTION on a MAC)
While holding down the CTL key, left click the object you want to be the child.
Right click - a drop down menu will pop up.
Left click on Add Parent.
To remove a parent
If an object has a parent, as noted in the outliner, you can remove a parent as simply as adding one.
Left click on the object you want to be the parent first.
Press the CTL key (OPTION on a MAC)
While holding down the CTL key, left click the object you want to be the child.
Right click - a drop down menu will pop up.
Left click on Remove Parent.