The document outlines the key steps in preprocessing text data: 1. Tokenization breaks text into individual words by removing punctuation and numbers and splitting on spaces. 2. Stop words, like "the" and "an", are removed to focus on meaningful words. 3. Stemming reduces words to their root form using an algorithm like Porter stemming. This groups related words together but does not always find the true root. 4. A vocabulary is created by taking the union of all words from all documents after stemming to prepare for further analysis.