Create a page where you'd like your sermon notes to appear, something easy to remember like "Notes" so that you can tell members to visit churchname.com/notes to access them. After you create the page, change the "Page Type" to "Notes".
Once this is completed you will not need to access this page again, so no need to add any blocks to the page or anything. Its primary purpose is to act as an easy redirect.
Head back to the dashboard and select the "Notes" card and then add a new note.
Create a note for the upcoming sermon and add whatever details you'd like for the user.
To add an "Add A Note" button, you can click the "Insert Note Editor" button at the top of the edit screen or you can type [note_editor] where you'd like to include a button.
If you'd like your sermon note to have a header image, just go to "Featured Image" at the bottom left of the editor and select the image you'd like to use.
If you haven't tried it yet, you can see an example of the Sermon Notes feature here.