Progress, bookmarks and per-book speed are saved automatically. Use Export progress in Settings to move them to another device.
Paste a direct link to an audio file, or a podcast or programme feed — one per line. A feed adds all of its episodes at once, with their titles and lengths. Ultima Thule, Musical Starstreams and the like publish feeds, so their feed address is all you need. A web page address will not work; it has to be the file or the feed itself.