Open demo.html to see a list of all the glyphs in your font along with their codes/ligatures.
To use the generated font in desktop programs, you can install the TTF font. In order to copy the character associated with each icon, refer to the text box at the bottom right corner of each glyph in demo.html. The character inside this text box may be invisible; but it can still be copied. See this guide for more info: https://icomoon.io/#docs/local-fonts
You won't need any of the files located under the demo-files directory when including the generated font in your own projects.
You can import selection.json back to the IcoMoon app using the Import Icons button (or via Main Menu → Manage Projects) to retrieve your icon selection.