Q. For example, you want to enable free shipping on all the products from category "Books".
A. You can set all the products in a category to "free shipping" by using "Search and Modify" checkbox in "Modify product" menu.
go to "Modify product"
select category in "Search in category" (ex. Books)
check "Search and Modify"
you will see the normal product modification page but with list of products in "Product list" section
that means you can apply any changes you make to all the products listed there
scroll down to "Free shipping"
change it to "Yes"
place a check in the box on the left from "Free shipping" setting - that means you want to apply this to all the listed products