twee is designed to take text files you write yourself and generate HTML files from them. This means that you can use any text editor you like to write your story. It's important that you use a text editor, however, that saves to plain text format (.txt). Using a word processor like Word or OpenOffice won't work.
The format of a twee source code file is very simple:
:: One Passage This is the body of a single passage. A passage title is set off by two colons at the start of a line.
You can place line breaks directly in the passage text.
:: A Second Passage [tag1 tag2]
You can leave as much space as you like between passages. Enclose tags with single square brackets on the same line as the passage title, separating them with spaces.
By convention, twee source files use a .tw file name suffix, but you don't have to follow this. You can save them with a .txt suffix instead if you like.