Story Mapping: How to write initial epics and user stories?

We are trying to do a story mapping session for a new project (a student portal).

Since this is my first time doing this and we don't have a business analyst in the team that could help me, I'm struggling with how to write the epics and the user stories. I've seen examples of these but for eCommerce or an email (example attached below).

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I would like to know how would you write the epics or user stories for a student portal? What would you write? has anyone here have experience with this that could provide me some initial map or idea?

For example: In our student portal students should login, go to classes, view school news, etc. How could this map to epics and user stories?