Here are a few suggestions that have been useful to me. Important caveat, I’m not a knowledgeable myocologist but I have some friend who are. These are mainly tips they provided me.
First, I recommend the book “Mushrooms of the Pacific Northwest” by Trudell and Ammirati. I realize you asked for online resources but this has been a mighty useful book and it does contain keys for the various classes of mushrooms, generally arranged by shape. You can always get a copy from your local library to check out. I bring it out in the filed.
Second, check out the website Mushroom Observer, you might start with this page:
How to Use Mushroom Observer, one thing about this site is that it does seem to be mainly western Washington.
Last, try to find someone knowledgeable in your area to help you learn. It makes a ton of difference to see things in the field as opposed to reading about them online or in a book.
Hope that helps and I look forward to reading other peoples answers to this interesting question.