Confused in lucene indexing, need some help

These are the steps of indexing in Lucene given in our syllabus-:

The first step says that it is creating an index whereas the last step says that it’s adding document to index.

What’s the difference between these two? Can I get an example.

Here’s what I think it should happen-:

  1. Collect all words from each documents. Lists it like-;

doc1=>word1,word2,WORD3….wordn

doc2=>word1,WORD2,word3….wordn

And so on.

  1. Analyse the words and remove various types of words as per analyzer, process them as per analyzer.

Say now what remains is-:

doc1=>word1,word3,…word(n-1)

doc2=>word2,…word(n-3)

  1. Done. Now you can make inverted index as well by converting this to inverted index.