If you do not already have an ArcGIS account, you will need to create one to get started. If you cannot get an institutional account, you can create a free public one. Note that free accounts have limited functionality and do not allow for embedding, incorporating audio clips, and creating image galleries.
To create your free account, click on "Sign In" in the upper right corner of the StoryMaps site, which will take you to the Esri sign-in page. Then click "Create a public account" and complete the account creation process.
Once you have signed into your account, click "New Story" in the top left corner to create your StoryMap.
From the "New story" dropdown, you can select "Start of scratch," so that your project has does not preexisting block styles in place, or you can choose to start with a "Sidecar," "Guided map tour," or "Explore map tour" content block types.
In the space where it says "Untitled," you can give your story a name. Feel free to add a subtitle as well. (You change them anytime, so feel free to use temporary ones.)
StoryMaps automatically saves, so there is no need to save after launching your new story or after making any changes.