What are the major diffrences between Shock Absorvers VS The Struts?

For example what are the diffrences in the following two products?
http://www.autopartswarehouse.com/se...294967269+5619
http://www.autopartswarehouse.com/se...294967269+5609

First link are to strut inserts, and second are to shock absorbers.

Now for example lets say I wanted to make my civic less stiff and more cussioned, for a softer ride, ever when lowered 2in

what should I do, is it a matter of difference between shocks and struts?