Ordinary SQLite vs FTS3 Tables

Question

I have some data that is already organized in an SQLite table for my app. When I wanted to implement search functionality to my app, I found that the Searchable Dictionary example uses a FTS3 virtual table. I've never work with FTS3 and I just want to know what the differences are. When they say that FTS3 "does not support column constraints and thus, cannot declare a primary key," does that mean I can't make a column a type (ie. text, integer, etc.)? How do I specify unique identifiers (id)? Should I manage/organize the data differently from an ordinary table? Is it meant to replace my original table if I want to implement search functionality with FTS3?