There are probably a million-and-one great writing apps out there for iOS, but if you’re just starting out on a tablet,
Google Docs is probably a good place to start. You can create documents, share them, edit them, and even save for offline use. Why start here? Google Docs is also available as a web app for desktop computers, meaning it’s easy to shift your writing efforts between devices. If you’re a bit more advanced and want to write using the Markdown language,
iA Writer is a popular choice.