Indexing in terms that my family can understand

In response to the weekly readings in our text, I chose to write about indexing. I have gone over this section countless times and this one section seems to be the one that I am having the most difficulty with. So, in terms that are easier to understand.
1. Indexing is done based on how terms are obtained or chosen.
2.There are two types of indexing: derivative indexing and assignment indexing. Derivative indexing, also known as keyword indexing, means that terms are derived from or taken from the document. Assignment indexing means that the terms are assigned to the document.
3.Assignment indexing uses a controlled vocabulary to choose appropriate terms. Derivative indexing or free indexing obtains the terms directly from the the text.
An example would be if someone was trying to find a recipe for pumpkin pie. Derivative indexing would allow the user to use the term pumpkin or certain ingredients to locate a specific recipe. Assignment indexing means that someone could look up types of pies to obtain the recipe of their choice.