There are a range of story map application templates, so you'll have to let us know which one you want to make.
You can build a Map Tour, Map Journal or Swipe/Spyglass story map directly from the Apps list on the Story Maps website: App List | Story Maps . On that page, click the 'Build' link next to the story map app you want to use. That page lists all of the story map application templates and also has step-by-step instructions for each of them.
To create a story map from inside ArcGIS Online, make sure you are logged in with any account type (you can't make a story map unless you are logged in), open the web map you want to use so you are looking at the map in the ArcGIS.com map viewer, then press the Share button and then in the dialog that appears choose the 'Share As Application' button. Then in the gallery of application templates that appears, click Publish next to the application template you want to use.
