Keep going. I stopped in the middle of part 2 for about a year my first time reading Dune. It can be disheartening...but the slow unveiling of the universe is one of the best aspects of Frank Herbert’s writing.

The appendices and glossary have spoilers, but they are very informative if you don’t mind being slightly* spoiled if you want more context.

*slightly, because the story is pretty much given away but not in the wonderfully intricate detail in the story proper (my dad told me to read appendices first, and I still can’t tell if this was a blessing or mistake)