You need to state which Twine application (1.x or 2.x) you are using, and if you are using Twine 2.x then you need to state if you are using the web-browser based release or the install-able release.
1. Twine 1.x application:
You can use the File > Export > Twee Source Code... menu items to obtain a text file containing all the passages of your project.
2. Twine 2.x Install-able release:
You can use the Twine > Show Library menu items to open the folder where the application stores the Story Project text based files. You can also use the Archive option to create a text file containing all the passages of all your story projects.
3. Twine 2.x web-browser based release:
You can use the Archive option to create a text file containing all the passages of all your story projects.
note: The content in the text files created in points 2 & 3 is structured, you will need to process that structure to extract the passage contents.