Column Type: text Column index:?

hmm. I am confused about this one. I am using a detailed page, and want this page to be indexed for searched, but when I choose Column Type: text, the system doesn't allow me to choose a Column Index.

I thought the field Column Index was how I told the system to search.

Can someone explain to me how I can have the system be able to search on this text?

Let's say the column is called "full_story"